Round-spoke styling (STYL.18) - BMW parts catalog You can buy them at a dealer. I'm guessing fig 5. P/N 36 13 6 768 640 getbmwparts.com has them for MSRP 14.25, cost $11.40. I assume that is for 1. You can probably find knockoffs cheaper but the Roundel will probably fade and flake off.
Little stuff like this is why I try to maintain a relationship with the dealer sales guys. I'd start there if you can with a line like, "Do you have an extra wheel insert laying around here?" It worked for me last year.
wheel caps I pulled one of the other caps and the logo is a sticker on a plastic insert. The rim says RADIUS and I find that is an aftermarket rim made by EXEL. An old rim that is not made anymore. Funny, I have seen lots of Beemers with like rims. So, (as suggested) going to the dealer when convenient, or the U-Pullit where there are lots of rims to measure. I did spend alot of time searching for the rims and a supplier, it just didn't play out. Thanks for the input, it got me to the bottom line. Mike