You've covered about every base I can think of.

I've found mushroom compost to be a pretty good product generally speaking, although it depends on the actual supplier in your area. The study I did this spring on quality of bagged compost here in central MO found the mushroom was above average and was priced in the middle of the pack.

I think you're setting your standards too high. It's hard enough to find a good source of compost, and even harder to find any for cheap, and in "choose your own quantities". I see you're in zone 5, so like me, your growing season is coming to an end soon, as fall approaches. May I suggest that you collect leaves this fall, en masse? I myself need some compost, but not until spring, so I plan to gather up leaves this fall, plus more for mulching. I plan to mulch them though, with my electric leaf blower/mulching vac. A lawnmower works well too. You have to find your equal ground, because it sounds like you don't want to pay the premium to buy in small quantity bags, but at the same time don't have the ability, or the desire, to buy in bulk. This is where leaves are perfect; you can collect them in as small a container as you like, and they are free! Check the curbsides this fall, because people pile up their leaves, and sometimes they are already mulched! Can't beat that!

Joe

If you are not planning on planting this Fall, I would stop every landscape truck I saw, and ask them to drop off their daily loads of grass clippings,leaves,,...etc etc, they do this every day, some are working 7 days a week, they could fill up your beds (lasagna style) in a couple of days... and then (if it was me ;-)
I would pile it real high on the beds (it's going to shrink...A lot ;-)
and then I would take more of what they are bringing you and make compost piles with it, it will cook down and be ready to amend your beds when necessary ;-)

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Great suggestions so far. Another thing you could do is start a worm bin. It'll produce very concentrated vermicompost (aka worm poop) that doesn't change soil composition like regular compost, but it feeds and builds up your micro critters like crazy. Your plants will love it.

Agree with other suggestions especially bag of grass clippings, leaves here and there. If you work outside the home, you can set up a tote in a break room or such and ask for any organic waste, coffee grounds and filters. Same goes for if you attend church or there are church breakfasts etc. Some folks go make the rounds at coffee houses. Some collect organic food scraps from restaurants, maybe one you frequent. If you prepare/cook food at home, if you are like me and prepare alot of fruits, veggies, eggs you will have lots of stuff from that. Don't forget the waste from your own garden clippings, deadheading, weeding.

Starbucks! My local shop hooked me up this summer.
Mix UCGs w/ shredded newspaper and enjoy.

Any of your neighbors (or yourself) got a bagging mower?

If all else fails, stretch the small amount of compost you have by making compost tea

Oh, one more thing: wait until November. You can probably find all sorts of compost material in bags in every neighborhood in Suburbia on Sunday evenings (just be polite and discreet).

dragonjaze if you gave the town or area where you live it would be a lot more helpful. Someone on here might know of someplace that could be of help.
Also may I suggest planting a cover crop or green manure.

Here are some other ideas for compost ingredients & it won't take too long for a pile to build either in place in the garden lasagna style or an out of the way place. Once covered with a uniform damp mulch of leaves or wood chips it will look good all winter with an occasional raking if desired.

-place a want ad on Craigslist for manures &/or spoiled hay OR borrow a friend's truck or larger vehicle (I use a Suburban with garbage bags inside garbage cans, so can load up a lot & still keep the vehicle clean.)

-want ad for sawdust, spent hops, used coffee grounds, coffee chaff (from a roaster), herbicide free grass clippings, food bank gleanings (I'm sure they toss spoiled produce), etc. I've found a coffee shop with an outside spot where they dump their coffee grounds or over roasted beans & you bring your own containers/shovel to haul away any time of the day.

-hay sweepings from a feed store where they sell grass hay, alfalfa hay & straw (once covered the occasional sprouts aren't a problem & just add to the mix)

-offer to pick up manure from your county or state fair as they have to pay to dispose of it there & may be wiling for you to come load up during a show or afterward (llama & rabbit can be used right away and are easy to scoop pellets)
Perhaps, a rabbit club in your area will be having a show or you could find someone who raises rabbits for show or 4-H. Chicken & sheep manures are also smaller volumes & easy to mix with browns to reduce the odor. Once covered up with other materials there is no manure smell.

-animal rescues with livestock or small anaimals such as guinea pigs use pelleted bedding (sawdust) that composts well with manures & has a uniform appearance. As long as the sawdust is mixed with something it doesn't compact & become a problem. I've mixed it with manure, used coffee grounds, or grass clippings for mixed borders and in my edible gardening beds (out of the growing season) with great results.

-people who can or juice vegetables & fruits have scraps. That was a good idea to ask co-workers & the fall fruit harvest is almost here with apples, pears, & plums, which when processed always have waste especially apples.

-restaurant or local cafe for food scraps

-farmer's market might be a good place to find a regular supply

-browns: household paper scraps, used tissues & napkins, paper towel & toilet paper rolls, cereal boxes, etc.

It may take awhile to make connections, but you never know what might appear. I've had llama walk past my driveway with the owner of course & she brought buckets of llama poo + coarse sand from their arena. Another gal I met on freecycle raises goats for milk & instead of taking a trailer full of spoiled goat hay bedding + manure & paying $10 to dump it at a recycler for him to compost she brings it to me about every 6 weeks to dump free.

When you make your contacts about the manures you could ask for their phone number or email to check back with them about when they would have more available for pick up. I have 2 places within 2 miles of me that I've used for several years now. I don't agree to take it all, but do say to contact me anytime they need to reduce the pile and that I'll contact them when I'm ready for more.

Hope that helps!