CD,
I went back and looked at the small spools I found which fit in the Two-Spool canister. It's sold under the "Dritz" brand. I haven't been able to check them out to see if they work as well as a wooden spool, but they're the same size. Because they're plastic, there's going to be a difference in weight. That may or may not represent a problem!
I walked through Wal-Mart this afternoon and noticed they still had several sets of the "sewing" kit. The kit also comes with some hand sewing needles (some of the longest I've ever seen) and a threader. There are about 10-12 spools in the kit, so it's worth the $1.97 (I think that's the price).
Jeanette