Following along because I also don’t have a source for the bark fines. Nor a source for partially composted pine bark that I could sift, though it pains me to even consider that. Not finding it in bags ( like 1-2 cu ft) that I could manage & keep getting as I need it.

Where do you live? Closest major city is fine.

this is what I use. Available in Colorado at some independent nurseries.

Sometimes the bag looks like this:

It is pine bark fines.

Popmama... I live near Sioux City,Iowa. But travel to Omaha, NE , Des Moines IA, and Minneapolis MN frequently

I did see a place in Omaha that carries some Mountain Magic products. Maybe you could call them to see if they have or can get Soil Pep. Indian Creek Nursery. If I see anything else I'll let you know!

I may have found something—a Kellogg’s product of a Planting Mix at a farther-away Home Depot. It may not be all bark but be a mix with finer peaty -like stuff, though. Don’t have time right now to go get a sample bag.

Off topic or on, but whatever brand of soil conditioner one is looking at, have you inquired with the mfr of the like on what the % is. I looked at one eon's ago, in search of fine and it was 60% peat, 10% bark fines, and the rest was compost. It was pricey , give that half the bag was peat and just 10% was fines.

In a pinch, if you have the access, you can buy some mini nuggets and chip it yourself

That Timberline mentioned in the OP seems to be only at the big box stores .Granted this stuff may be regionally produced and may vary, but the Timberline stuff I've seen at the local Lowes, etc - is more lke 70%'ish bark with quite a bit of sapwood in it in the. In the Bark Mulch, it looks like the percentage of sapwood is even more fwiw