As far as 5th wheel components are concerned, more specifically; tires, axles, bearings, springs, and hubs. The 5th wheel and travel trailer community often overlooks the industrial community where products and services are provided at better pricing and and better reliability.
As a former industrial sales rep, I hardly ever do business with consumer outlets if I can get it through a industrial commercial supplier.
"Just in time" marketing, requires warehouses full of goods just waiting to be purchased and delivered to local suppliers. In my area San Antonio and Austin are small compared to Houston, Dallas and the El Paso, Tx/Juarez Mexico markets and we have everything here and they dang sure have everything there.
When you are buying goods and services not specifically for an RV, you are getting cheap parts, and poor service. The Sailun tires bought locally by the OP were destined to be on a truck somewhere until they were diverted to a life of luxury mounted to one of our rigs.
I hope that others will start looking at the industrial sector as a good back up to using RV dealers and consumer outlets. Although the OP found the tire at a consumer outlet, it was available in his town because of industry not for RVs.
PS as soon as I get these taxes done and the Oak leaves raked up, Im going to get a set of Timken bearing and CR seals for my rig. Im going to do a great hand pack job, and insure that my spindle nuts are adequately secured. I will get them off the internet or an industrial supplier here in SA. I wont be buying them at an RV dealer or northern tool or even an auto parts store.