If you're fortunate enough to have a motorcycle salvage yard in your area, or a yard with a motorcycle section, check out the great mirrors that MCs have. They can be easily adapted to 7/8" handlebars and they are designed for 2 wheeled vehicles that are driven on the streets. They're usually cheap too; a couple of bucks for a nice chrome mirror with a convex lens that gives a good wide angle view of what's sneaking up on you.
I've never had one made for a bicycle that was worth a darn.
Tom