That's the most popular style it seems. I saw some 4" round "bullet mirrors" on eBay. I also consider a small 55-57 GM mirror.
Or the early 70s truck "sport mirror"
70 71 72 Chevy Truck Square Rectangle Chrome Outside Rearview Door Mirrors Pair
http://r.ebay.com/cVobw2
55-57 Chevy 50-63 GM Door Fender Outside Rearview Mirrors Pontiac Oldsmobile PR
http://r.ebay.com/e8n3sn
4 Bullet Race Sports Car GT Racing Chrome Side Exterior Mirror Hot Rat Rod Pair
http://r.ebay.com/9g1FLE
People ditch the 3 leg towing mirror in droves even though it is considered "correct". I'll run wtfe I want and THAT will be "correct" for me!
In Oklahoma only a mirror on the driver side is required. Check local laws when modifying federally-mandated safety equipment.
I do not like the hooptie lookin ones we have....

. I would have ditched my tripods too!