I have had pretty good luck getting tractor parts at my local NAPA. Just recently NAPA has started replacing their knowledgeable counter help with computer looker uppers and I have to explain to them what I want (had to spell Heli Coil to the lady twice). That said if you can get them to find it they do have a paper Ag and industrial catalog that helps a lot. We also have an American Standard parts store and they are pretty knowledgeable too but Pep Boys, Auto Zone, etc is worthless for tractor realted stuff. If its not an automobile that is listed in their computer they are sunk.
Try NAPA and ask for a starter solenoid, I think '65 is pre relay.