Actually the link by audiodog is the way to go
Yes, KTI airless tires happens to be in Oceanside, CA, very close to where I live and I stopped by to visit them today. I was able to check and touch and feel and get an idea of them. I think they are good. I asked the president a bunch of questions about them and he also refered me to the first website on this blog to get them at retail
www.airfreetires.com. Later on my visit to KTI an assistant helped me further and showed me how to mount them. You need to get their special tool. Believe me. A screw driver might work, but you might damage the tire. Also, if you take them out of the rim and reinstall them, it is very important to check if they did not stretch when taking them out of the rim and loose their thight fit to the rim. And it is very important to use the right rim width and type for the particular tire of your choice. Remember there is no air pressure to press the tire against the rim...so it is all on how good the molded rubber fits the width, depth and flange shape of your rim.
There are two different rubber formulations. One has more bounce. And the tires come in different weights to match your desired comparable PSI on a normal tire. They are available in almost all basic colors colors Blue, bk, R, Y, Grey and white. There is a link here to a list of other airless tire manufactures as well:
http://www.airfreetires.com/Competition/
In summary, if thorns are an issue in your area( and actually I know of one particular place like that), this is an option to consider. They might not offer all the thousands of choices on threads you can find on regular air tires, but I just thought one thing about the airless that makes them really appealing(besides being flat proof); this is if you have some time and patience you could cut threads yourself if needed; and there is no limit, because the whole thing is solid. Get a fatter sort of slick one and you could cut them into Knoby Tires!
If people build their own model airplnes...why not to build your own threads?
Have fun.