your looking for the same thing i am. but i am looking for a cap for a set of 3 piece wheels for a ferrari. i ordered one from a local race shop. they found a company in florida i believe that made those caps for speedline here in the U.S. i will ask the name of the place when i pick my cap up and pass the info along to you.
do a search online for a shop called speedline motorsports out of redmond,washington. they were able to get a hub and cap for my speedline wheels that are on my ferrari. with shipping it came out to about $80. if you cant find it let me know and i will get you the number.