Not trying to be a wise guy. Just trying to help you make informed decisions while tire shopping. All I meant to say was that recommended tire pressure isn't an indicator of carrying capabilites...

the reason you cant find the tires you want is because you are in an extreme minority of the worlds population that has found a reason to have a 20 inch bicycle wheel carry so much weight (and for so many miles, so often). Most people who need to transport that much weight would rather have a trailer or a trike (becuase nobody wants to tip over with 200 pounds of whatever it is that they might be biking around with). and most people would rather let a motor pull/push it. Mopeds are cheap and a hell of a lot more powerful than human legs. Trikes/trailers can spread the load, and don't fall over...

But regardless apparently all you have to do is find 999 other people who want the tire you want and you're good to go. Not a bad offer after nothing more than a phone call. Start a facebook group or something if you're this concerned about it and so convinced that the people of the world want this to happen but are being ignored.