I know how you could make 45 "different" shops. Put each item that you want to buy in the 15 shops. Then, for the items you want to make unpurchasable, make the floor unwalkable in that area. Then put a table or something on layer 5 or 6 so it appears there is only 1 item you can buy.

Monopoly has 28 buyable deeds, so you could just put two items in each shop (the left and right sides, leave the middle blank). So let's say your first shop type has Mediterranean, blank, and Baltic. In one room, you can buy only Mediterranean. In the next, you can buy only Baltic. Etc.

With three "deeds" per shop, you'll need 9 and 1/3 shops. You could use the other 5 2/3 for other things, if needed.