Why are my trailer tires so hard to find in San Antonio?

I'm going to take the longest trip I've ever taken with the Colby T this summer. I was checking my tires today and noticed that one of them was made in 2009, even though the Colby T was purchased brand new four years ago. It had been the spare until a few months ago when I had a blow out and used it thinking it was as new as the one I bought for a replacement. The tread is fine and all, but I just don't like the idea of traveling across the country with a seven-year-old tire. I've seen what a blowout can do. I was extremely lucky that I didn't suffer more damage the last time. There was some "minor" shredding of the undercoat, but none of my pipes or hoses where damaged.

I decided to go ahead and replace the tire. I started calling around town looking for one in stock somewhere. Even tried the Goodyear RV tire site to see where they think it is available. No luck. I remember having a similarly hard time finding one that last time.

I ended up ordering one from Amazon already mounted on a rim for the same price it would have cost to have one shipped to a local store. It kind of scares me about being on the road. How long will I be stuck looking for a new tire, if I need one during a trip?

Has anyone else had trouble finding tires? Or, is that just the price I have to pay for having such a little trailer?