If you can't wait for Superformance to restock then this company in Germany have them for £148 +VAT and postage
http://www.dinoparts.eu/EN/ferrari-2.../hub-cap-more/
or this one in Italy whose price is "on application"
https://www.autoepoca.it/brands/ferr.../wheels-bolts/
As for who supply Superformance, I have no idea. I know they do use China as a source as some boot / bonnet levers I bought from them were wrapped in Chinese newspaper.
Neil