autometer has them and I find them on ebay most of the time. They have two styles, One had a probe that protrudes past threaded part and one that is just the threads. Cylinder head temp sending unit and make sure short or long sweep matches gauge you are using. I think about 15 bucks per unit on ebay. They have cpl listed now.
Like stated if you want multiple points you can wire in 3 position switch with middle pole to gauge and upper to one sending unit and lower to another unit. Flip back and forth between two readings.