Below is a picture of one I just made for the USAF Strato Blue M151A2 I sold.
The discs are Lexan, 17" diameter, with stainless steel fasteners so rust won't stain the art. The springs that hold it to the tire are steel.
I can produce these for most any unit insignia. I have the images, just let me know what you want on it. Text can be added.
Custom art or your own image may be a bit more to duplicate, but most of these will ship complete for $75 - $100 plus shipping. Just PM me with your ideas and I'll get you a quote.
