Hi-- we just bought a house built in the 20's and there is a 2-piece toilet that had a tank that mounted (at normal height) on the wall. This is in an old bedroom above the garage, and the owners removed the wall tank (and stopped using the bathroom) because the bolts holding the tank on rusted, and caused water to tilt forward and spill (and they didn't use this bathroom anyway). We want to restore it to use (as an art studio) and our plumber said we need to find a replacement tank because for a number of reaons replacing the whole toilet is very complicated in this case (we agree with him, won't bore you with the details). We JUST need a replacement wall-mounted tank that will work with the other part of the toilet. Any ideas where to find one?

There is quite an assortment in a wide range of prices listed here:
http://www.nextag.com/wall-mounted-toilet/search-html

Try a google search or Ebay. Folks are always selling this stuff for a good price.
You just need to be sure that the tank is the 5 gallon size so the toilet will properly flush.