As for seed companies, I have been using rareseeds dot com and am pleased after three years of ordering...mostly veggies, but have ordered some flowers.

I've not really seen any companies actively marketing 'flowers for bees' After year one with a hive, I'd comment that any wildflower mix that works for your zone/region should help.

I'd suggest just planting whatever flowers you like--the bees will find them. Our bees, here in Central Texas, are particularly fond of borage, monarda, lantana, goldenrod, mesquite, and our antique or own-root roses. They do a good job pollinating anything that blooms in the vegetable and herb gardens, too.
We have two hives, and are hoping to add two more in the spring. Bees forage in a two-mile radius, so whatever your neighbors have, the bees will enjoy, also.