To follow up on Elgin's Unimportant Responses idea, take a look at this one:
http://forums.usfirst.org/showthread.php?t=1508
It's a little surprising that this question was asked six times, and it still wasn't really answered. I'm guessing that most teams have figured out that stores do indeed sell sprockets, but that they're interested in buying the exact sprockets that are in the kit, so they don't have to do "minor additional machining (broaching keyways, enlarging bores, etc.)". Is there any reason for FIRST to be beating around the bush with this one?