If you're close to the Terre Haute area, try Elliot and Sons in Tecumseh. They're about 6 miles north of Terre Haute on 63. very large yard and heavy on older iron. I don't recall seeing any 1/2 ton ADs the last time I was there, but there could be one back there. Be prepared to clim, though, as most of the good stuff (read old) is up at the top of the hill. Nice loooong climb, too.
