We have soil similar to yours, with a pH around 7.6. However, our soil does contain significant organic material, unlike the soil that your landscaper put down. It could be soil from a working farm, soil that has been plowed and planted every spring for a century or so. If that is the case, adding compost should improve the soil. Did you make your own compost? Some commercial sources of compost include grasses that have been exposed to weedkiller. Such compost really needs an additional year in the pile, before it is safe to use. If you want to apply nitrogen, without raising the level of phosphorous and potassium, then you could apply ammonium nitrate mixed with water. I would be cautious with this, to avoid fertilizer burn.

Urea and ammonium sulfate are two fertilizers that are often available at garden stores or big box stores and both have no P of K. Urea is very high in N (usually around 46%) so you only need about 2 lbs per 1000 sq ft (easy to overdo).

7.6 is a very high pH for lawns and gardens. I wouldn't try to drop it using sulfur in the lawn because it's not practical. But you can certainly dig some into the soil in the gardens and flower beds (it won't help much if it's just spread on the surface because too much gets lost into the atmosphere).

Adding a lot of compost to a planting hole may seem like a good idea, but it can backfire because it changes the structure of the soil too much in that one spot. So the plant roots don't spread to the soil around it (it's not good enough) and water can collect there in a bathtub effect if the surrounding soil is clay. It's usually better to amend a whole bed or to simply top dress with the compost and let the soil microbes and worms work it into the soil over time.

Most all plants grow best in a soil pH in the 6.2 to 6.8 range where most all soil nutrients are most readily available and the recommendation that you spread, and work into the soil, 3.5 pounds of sulfur per 100 square feet will, eventually lower that soil pH. Your soil has ample available nutrients for your plants now and the last thing you would want to do is put some nitrogen, that would encourage green growth that most likely would not harden before winter, down.
Use the resources you will be getting in a few weeks to get the level of organic matter in your soil built up and think about maybe gettng some liquid "fertilizer" to use next spring.

Agents remarks: "pH is very high. Drop by applying 3.5 pounds of sulfur/100 sq.ft. and scratch into soil. Nutrients are acceptable - no need for fertilizer at this time. As new plants emerge in the spring, apply a water soluable fertilizer."

You need to find some "soil sulfur", sprinkle it evenly at the rate they suggest, and rake it into the dirt. It will lower the pH a bit.

everything I read of applying sulfur says that in order for it to really work to lower the pH it must be dug in well, not just scratched into the surface.

The practice here, where the dirt is really alkaline, is to spread soil sulfur liberally, rake it in (or not) and water the heck out of it. It dissolves and the water carries it down into the dirt.

Now a little more than two months later, there is hardly anything in bloom.

When you transplant things from nursery pots to a landscape, they tend to do little or nothing for the first months or year because they are putting their energy into root growth.

Chill out, trust the guys who did the soil testing, add the sulfur like they told you to and relax. If you start forcing growth in September by fertilizing the plants they are even more likely to suffer in the winter.