Maxxis makes their radial trailer tire, the M8008, in a 13"
https://www.maxxis.com/catalog/tire-...t-radial-m8008. Many good reviews on this tire. They're the ones I run on my 15" wheels. That's the route I would go if I were you. Most tire shops can order them.
With those weights, you probably have two 2000 lb axles on there, so even load range C tires will be fine.