There are .338LM semi's that look a lot like AR's to me.
Cobb Mfg. used to make an M100 through M400 IIRC, and each was bigger and would accept larger rounds. It was also modular. Anyway, I'm positive one or more of them did what you want. But just like other companies and projects they bought out, it died the moment Bushmaster got their hands on it. Can't tell you how well they worked, if it's worth hunting one down, etc.
Olympic Arms (yeah, I know) makes/made short magnums for regular AR platforms, but I forget which ones. I wouldn't want the rifle anyway, but if they can make it I'm sure you can.
You could probably use the AR10 platform to build your own. If the round will fit in a magazine somehow and feed in to the barrel (may take some tweaking and custom work) I'm sure it would work. Back when .50Beo and a few other large bore AR chambers were getting popular, Tromix I think built a .458WinMag and/or .450Marlin off an AR10. Expect it to show more wear and tear than other rifles, because like the .50Beo, I'm sure any hard recoiling round isn't good for some of the parts, most notably the bolt lugs (which you may need custom cut?). You may think it wise to use heavier duty receivers, but all the lugs and such are practically identical so with the Beo, I just used a Mega lower. If it beats up the AA upper or Mega lower, I'll just swap 'em out. I don't shoot the Beo much though, so it's never been a problem.
Contacting Tromix and seeing what they did would probably be a good idea and you may learn something about doing it.
Unless buying a factory rifle that works and one with a warranty, like said above, it probably wouldn't be worth it as it would probably malfunction more often than not.