Great question. I did the same research last year.
Here you go for sharing.
1) I want to paint my caliper silver to make it stand out a little as black just blends in with my rims.
(Red color may clash with my exterior color and Yellow calipers will stand out too much for my car.
2) I went to two powder coating place. I was told they dont do high temp powder coating for calipers so my best bet is to use high temp paint such as duplicolor.
I bought the high temp Duplicolor silver spray paint but haven gotten around to doing this mod yet as it is still too cold and too damp here in Seattle area.
3) I searched on Ebay and searched on line. None of them make M badge sized perfectly for our calipers.
4) So I measurde my calipers, searched on line for a good shop that makes high temp decals and found Grafixpressions.
Click here:
They make very high quality decals, does a very good job and excellent customer service.
5) I had them make me six of gray colored M badge and two silver. See attached photos.
I hope to get my calipers painted this summer and have the M-badge I had custom made installed.
Contact Graphix... above for quote.
Here are photos for size of our caliper, and M badge that I had custom made for my M6.
Hope that helps.