1) Thermistors can have different resistance ranges, but are generally a fairly standard item.
Question is what did it do previously? There can be other reasons for that indication.
2) Generally a thermostat is required to get the engine to run hot under general running conditions. If water was boiling in the engine, there was another reason, not no thermostat. Not a clue as to souce of a suitable 'stat, but an agco dealer might be a good start, or maybe a truck centre, or you local agri-dealer, even.