Need window balances/weights for 20 year old Anderson windows.

We need to find replacement balances for 20 year old Anderson windows in a house we bought. I have submitted a picture. The topside of the balance reads 1600-17. The lip reads 1131, as well as the number 1 alone, then B1135, a space, then an 8, another space then 92. So 1131 1 B1135 8 92. The back side reads 11600A-3. There are no other stamps. Thank you for any help.