Who sells Bougainvillea in the Philadelphia area?
Bougainvillea is not hardy, thus it is not usually grown locally. Bougainvillea should start being available in nurseries in a few weeks. You can try Meadowbrook Farm, 215-887-5900, Meadowbrook, PA. which is affiliated with PHS. Home Depot carries them, and Lowes might also.
Mail Order through the web (Logee's Greenhouses for example) will give you more choices, but they will be smaller in size, facilitating shipping.