I love the racy look of the Raydyot mirrors, but they aren't real practical out on the road. I have three of them spread across the dash, but they have a limited field of vision.
A few years ago at Concorso Italiano, I discovered Aardvark International - the US distributor for Talbot mirrors. They had convex elements for round Talbot mirrors that I installed in my Raydyot mirrors.
These were a little smaller in diameter, but they will fit in the Raydyot housing.
Talbot & Co.
More recently, I purchased a clip-on CIPA mirror at Summit Racing, and modified it to work with my Raydyot mirror.
The CIPA mirror has two plastic fixed posts, and two spring-loaded metal posts. I trimmed the plastic posts to reduce their width, and then bent the metal posts at an angle so they would clamp on to a round mirror.
The results are great - I can drive with this clip-on mirror in place, and when I get to a show, I just pull it off. Affords a much better view of what's behind you.
http://www.summitracing.com/parts/cip-34000/overview/
regards,
Jeff