I don't know much about loupes, but there are a few companies out there that make them, including Zeiss, Designs For Vision, and Surgical Acuity. I would Google those and look at their websites. You may be able to have them build your prescription into them and then you would be covered. Also, there is a loupes discussion in the resident forum (where I got this info) that you may get some more information.
Hope this helps.