Here is a 13" load range "D" (1650# per tire).
The thing is, if you go from load range "B" or "C", you may have to go with a tire and wheel. The wheel has to be rated for load range "D" also. Do your research. The only way the find the weight rating on your current wheels may be to dismount one of the tires. Most trailer wheels have the weight rating on the inside of the wheel. You may get lucky and find the weight rating stamped on the outside of the wheel somewhere. The weight stamped in the wheel must be higher than the weight rating of the tire.
https://www.etrailer.com/Trailer-Tir...a/AM31990.html