My wife and I have been buying prescription sunglasses mail order from
Hidalgo Inc. for about 15 years.  They offer a wide range of frames from
Ray-Ban to Randolph (military supplier) to many specialty types
including Titanium and Carbon Fiber.  Their catalog has a very detailed
Guide to Selecting Sunglasses comparing glass, plastic, tints, bifocal
types etc. if you really want to "go to school" on the subject.  They
also had very competitive prices and excellent service, even parts for
frames.

I understand the company recently relocated and may have changed owners
maybe for the better or ???  You can call them at 318 619-9509 for a
catalog.  

Steve Colwell