I've found these a little hard to find as well. My local hardware store has them in boxes of 10 for something like $1.50 each, which is a little high.
However, I've been able to find the 0.250 quick-disconnects for much cheaper. I bought a box of 50 of them at the same hardware store for only $3. I'm probably crazy for doing this, but I just give them a very slight crush with a pair of pliers before putting them on the switches, and they stay just fine. You can't crush them too much, though, or they won't fit at all.