get it running, rebuild the brakes... somehow you can always find a use for a truck when it is safe to use and runs.
a lot of the mechanical parts like brakes and gaskets, you can still buy from your local parts stores. you might have to order it, but usually they can get it.
if the regular stores can't get it, then look for the older farm/utility truck type parts stores in your area.
you can do a lot to bring it back for use on the farm without tearing it completely apart.
-W