I read almost exactly the same thing in a posting online, but I tried a couple places with no luck. Sam's Club processes film, but they said that they don't get much 35mm, and they use those canisters for chemical tests on their equipment. Walgreen's said that somebody else had come in earlier and gotten the few they had.

I bought 146 oval Advantix canisters and lids for about 9 cents each after shipping -- I think they'll be more comfortable in a pocket than the round canisters, and it was worth it to me not to continue searching. I'm not sure that I'll ever use all those canisters, but I'm sure I'll find other uses for some of them.