How about a local hobby store? They might be able to get them because they are not vehicle specific.
There is also the Proline Moab 2.2 tires that is about the same size as the Mashers.

The only reason that I have suggested the Mashers or Moabs is because they are the biggest 2.2 tires that I know of. Imex might have taller, they don't post the dimensions on their website.
http://imex.clodparts.com/

rolland