Could your regular optometrist make some for you? Mine has offered to make some for me and he did my prescription lenses for my Bolle inserts.
I've also used this site to take old glasses frames and have new prescription lenses put in them and I think they will do sunglasses as well. The glasses turned out great and cost about $100 for scratch resistant Trivex replacement lenses. I could have got them cheaper but I'm a big Trivex lens fan and they are more expensive.