Carloline,
I bought one from a artists / fountain pen store in Phoenix, and the other here in Springfield at a jewelery shop as far as I can remember. Both of mine are 10 power. You might try Hobby Lobby if there's one near you.
I know what you mean about not being able to read small stuff any more. Being near sighted I used to be able to read really tiny stuff, now I can hardly see it.
Joe