I once bought a single 10' length of 10" PVC from EMCO ... mind you this was in Calgary and it was a few years ago but anyhow, they did sell to me, I'm sure they'll deal with you. I felt like an idiot driving off with this one piece of honking big pipe strapped to my roof, but that's another story.
It won't work to get you a gate valve for tomorrow, but you could mail-order from here:
http://www.usplastic.com/catalog/var...ant%5Fid=19246
Anyhow best of luck!