Walking down Main Street on the left side, there are some "alleyways" called "gades". They are like little courtyards with shops and restaurants.
There is one that has a bin of maps just as you walk in - you can see them from the street. Sorry I don't actually know the name of the shop. They have lots of old maps, photos, and prints of the island. The one I'm thinking of has a bin like you find in art shops or framing shops - you flip through the maps. They have all sizes.
Just remembered that there is a shop called "Pirate's Cove" just kiddy-corner from the Post Office. They have the usual souvenier stuff but the back room has some old maps. Think it's a blue sign. I'm sure if you ask any of the shop people they can steer you in the right direction.
The shop (if you can call it that) is located in the alley next to AH Reise. They sell reproductions of old maps, photos etc. The ladies that run it are sweethearts and will let you browse to your hearts content.
Now you know where I hang out while Gram shops for perfume in AH Reise. I always buy a post card or print and get it framed for our collection in the family room.
Want another little St Thomas shopping secret? Go across the street to Little Switzerland. Go to the back of the store and up the stairs. There you will find four useful things 1) their sale counter, 2) a quiet coffee /snack shop , airconditioned, reasonably priced, comfortable, 3) clean uncrowded bathrooms and, the best last, 4) a FREE
internet cafe. Time can be limited if crowded to 10 or 15 minutes, but it is free and actually not usually crowded.
You will not believe that you are only 20 feet above all the noise and crowds.