I ordered 25 from my state DNR's nursery. They all showed up alive. I killed them through a combination of grafting experiments trying to make pink dogwoods and figuring out the trials of trees in pots.

I am unclear about what you mean by "specialize in". Are you interested in the generic species, like what toronado got from the DNR? Or are you interested in unusual specimens such as particular size, flower color, disease resistance or variegated foliage?

Yes, I apologize, my first question wasn't very clear. Pretend I never asked that, and instead let me ask another: Are there any white-bracted cultivars that withstand direct sun especially well? I know some straight species seem to do great in full sun and then others not so much. I'm sure soil and supply of moisture play a large role as well. I'm planning on getting two C. florida to go in my backyard where they will receive full sun from about 10-6ish.

The species will withstand full sun. I believe the missouri state nursery has them for a pretty good price.