VintageRob:
I posted the same query a week or to ago, expecting people to reply that BillyBob's Italian Motor Supply carries them for $12.95 a set.
Instead I got one reply that essentially said: "good luck!"
So, I guess these things are pretty scarce! Still, I have to believe that an Alfa logo for a Turbina wheel (which the US parts suppliers DO sell) glued to an aftermarket wheel center cap, would make an acceptable substitute. Unfortunately, no one seems to have fooled around with this. I guess it's up to you and I.