I found an online site that makes CUSTOM WHEEL CENTER CAPS. I just sent them an email with what I wanted. They are sort of flexible, domed stickers. They will do most sizes, I went with 60mm.
This is from their website:
Q: What are 3D stickers made of?
A: 3D stickers are made of high quality vinyl, with printed image on it, and covered with layer of liquid resin (2-3mm). This layer protects the sticker from external influence such as rain, solar radiation, and ext.
They cost $15.99 plus $3.00 for shipping. For $18.99 it was well worth it. It did take 2 weeks to get here from the Ukraine.