Heh, thanks. But to be clear, there's no shortage of caps available online; it's just that, when I check for compatibility, they all say no. The yeggi results don't seem much different in that respect -- no explicit compatibility checker, but no "i-MiEV" mentioned, either.
I was hoping someone could tell me "Yeah, a cap for a BrandX ModelY will work," or "an old film canister lid is a perfect fit." But, I realize I'll probably have to go on that adventure myself...