^^I think you can buy them in most fishy stores!!

, ive read about people growing them themselves actually...That's a nice cheap way to do it i think..Perhaps not in the same tank though, as i think it can get a bit out of control. Googling it will probably yeald useful information!
http://www.dwarfpuffers.com/care1.htm, there are a couple of articles down the bottomish end of the page that may be useful!Goodluck! I'm going to get a puffer soon! I cant wait, they're so cool!

Little doggy faces! Hehe!