Of course it all depends on where in the country you are but there really are thousands of truck tire mobile services that can take care of you within minutes if you have a spare, or in a couple hours if you don't.
Then there are the areas where the tire shops are a bit less than ethical. I'd hope those are the minority.
When I had a blow out in the middle of Canada, I had the spare put on, then when I got to Prince George, I bought two spare tires, used, from the local Goodyear store. And sold them on eBay when I got back to the US. Carried them as insurance.
When I needed a new rim, I just stopped at junk yards along the way. Google helps find them. Found many 19.5 rims. Now I have 22.5 wheels and haven't checked yet, but should find those at a junk yard too. All you do to test them is roll them on a flat piece of cement, if they don't wobble or act weirdly unbalanced (like your MIL), they're good to go.