Local nurseries may sometimes carry it. You can also check out eBay for plants and seeds--as well as many other passiflora. Or, you can order from any number of online nurseries that carry passiflora. Here are a few:

http://www.logees.com
http://www.gkexoticplants.com
http://www.glasshouseworks.com/trop-p.html
http://www.rarexoticseeds.com/Graines_de_Passiflora_Seeds.html

They like well-drained soil and lots of sun (although you will want to gradually expose them to sun to harden them off, otherwise you may burn your plants). The biggest thing to keep in mind is to not over-water them. Other than that, they've tough plants and will tolerate lots of abuse and keep coming back for more.

If you try to grow from seeds, keep in mind that these plants are stubborn when it comes to germination. It normally takes a month or more--some case up to a year--for seeds to sprout!