It may be hard to find a compatible tank unless it is a fairly new toilet. If you could find an exact match, it shouldn't be a problem. You probably would want to use new washers and seals, though, and those might be hard to find as well (unless the model is still being made). While you are at it, replace the supply line and the guts, those should only add maybe $10, and why put the old stuff back in. Last, though, repair parts are often pretty expensive, and it may just make more sense to replace it with a new one...lots of people here, including myself, like the Toto brand - the largest toilet manufacturer in the world (they have a US factory in Georgia, along with numerous places around the world).