fdbieker ... you might want to start your own thread, but I'll answer. There are several sites online that can help you ... here's one.
https://www.etrailer.com/question-224644.html Lippert Components is another.
No matter who you go with, do the measurement as laid out in the web link so you'll know your dimensions when calling. About any reputable spring and axle shop can make or get you the springs you need. Usually there is a sticker on the back of your axles that state what size you have. Some times it's stamped into the axle tube itself. D60 is 6000# axles ... D70 is 7000# axles ...
Danand Brenda ... when you are figuring what is sitting on your axles, don't forget that there is 2-3+ thousand pounds sitting on your truck or front landing gear that is taken off your axle load. Also unless you pull with everything you and the rest of the family own onboard ... you'll not be near gvw.