Amazon carries RV & truck tires these days. And if you're a Prime member, the shipping is 5 days, and free. The 22.5's I bought in June would have cost me an extra $100 per tire from other online retailers if not for the free shipping.
I used 19.5 Double Coin steer tires on my previous RV and they did fine. They saved me a lot of money too, at a time when I needed to save money. Later switched to Bridgestone. Also a very good tire.
Here's a few different brands:
Tires!