Anybody have a source for used truck parts including body parts, engine, ect.... for Mack MR chassie

Take a drive by the docks in any southern port city, you're bound to find numerous MR chassis' that had recently had their pumps removed.  you can likely secure a 2000 or newer chassis and upgrade an 80's chassis by re-trucking.  Or wait a bit and hit the upcoming BB auctions, and buy a different pump altogether.

looking more for future ref. like truck junk yards ect...  Live in Montana so checking on docks is not much of an option.

I think you're SOL.  Most MR's (think garbage trucks) have been through the wringer by the time they are retired, so the used parts are well worn themsleves.