This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From: msjohnso@KS.Symbios.COM (Mark Johnson)
RatShack is fine for clips...and they have a wide collection of sizes. My
suggestion, having been-there-done-that and replaced clips on several
controllers almost annually, is NOT to buy the little 3/4 inch copper clips.
They're too delicate for my tastes. Instead, I get the chrome plated ones
about 1 1/4 inches long, preferably with the little plastic grips on the
"handles." These are bigger and thus easier to manipulate while wearing
gloves, or when your hands are cold and unsteady.
If you use your launch system frequently, I recommend at least annual
replacement of the clips. This is more true of a club system than an
individual one, but remember that you take your choice of corrosives with
model rocket motors -- black powder leaves just a bit of sulfuric acid in
its wake, and composites drop hydrochloric. The clip bodies of copper
micro-clips will hold up OK, but the spring that holds the jaws shut is
steel and will eventually corrode away, as you've seen.