On my mirror caps, I started by cleaning them thoroughly in the kitchen sink. Between the dawn soap and simple green it got clean. Afterwards I dried and primered them. Then I sanded the primer down with 400 grit sandpaper, and cleaned it all up with alcohol and a rag. Then I sprayed ~5-6 coats of paint, about ~15-20 minutes between coats. I let them sit afterwards for a few hours and then clear-coated them. They were fully cured in about a week. Best advice is to take your time and DO NOT RUSH. Came out great.
I got the spray-bombs mixed from ebay, the listing I used is not there anymore but you may be able to find someone on there still. The cans that came were from Sherwin Williams so you could probably go to one of their stores and get one mixed.
A little pricey but the color was exact and you get a standard 12oz. can (I think the ones from the dealer are smaller). Between my mirror caps and painting my antenna base, I went through about 1 can.
Mine were not tow mirrors, but the process should be relatively the same. I would suggest sanding down any chrome as a first step...