I got mine ar radioshack...but...really they aren't that cheap there. The small ones do come in a package of like 4 (2 red 2 black). I got those...and one of those NOS looking button (big red as I call it) cost as much as those four. The 4 small ones all crapped out on me...2 work...not well if I may say so because they get jammed and the others melted away from the soldering iron (I would say I soldered the wires a couple times tho...to test stuff...).
Also, if you get the small ones...don't bend the pins like I did. I drilled the hold too close to the motherboard and it kept touching so I had to bend the pins on the small ones (the big one works fine...but...now I have a big one, and a lil button in my controller.....atleast it works huh?)
btw, im using the no chip rapidfire mod.