Interesting question.
I've heard (from Kim and 'Chelle) that the bolts used on the Urraco are Fiat bolts. Doubt the Jalpa differs from the Urraco in this regard (in terms of size, thread, length etc.). I've been toying w/ new bolts as well, but they're far down my list at the moment :-).
You might try International or one of the other Fiat supply folks (Bayless or Bruce's for example) and order a few and see. They can always be returned, but you'll pay shipping (both ways likely).
Better yet, determine the measurements and call and ask about the Fiat bolts first. Bayless responds well to emails.
Let us know :-) I for one am quite interested (okay and lazy since I haven't done this myself ...)
Btw, FWIW - the bolt pattern does match BMW - 5 x 120mm if memory serves, but the offset on my car is 0. Bimmer replacement wheels seem to (typically) have more of an offset (unless you go modular) ...
Regards,
Bryan
'74 P250S S/N 15622
Indianapolis Indiana USA
blissinindy@yahoo.com