If you want the name brand Optivisor, Squadron, Mega Hobbies, and Sprue Brothers sell them. I'm sure Amazon does too.
That said - consider the reading glasses. I've worn prescription glasses since I was 15, I'm near sighted, so when I was younger, I took my glasses off the work on models. But now I'm 51, and my closeup vision has suffered. Yes, I have bifocals, but they still weren't working for modeling. Never even considered readers - but one day in Walmart, I just decided to slip on a pair - I was amazed ! I bought some 1.5's, and 3.0's.
I wear the 1.5's most of the time, and 3.0's for small stuff. When teamed up with optivisor - it's like looking through a microscope!
Scott