EDIT: Pictures posted with my phone on the go.
Top photo: Cheap ebay or amazon sensor, 1/4" OD waterproof stainless end, mates right up to MPT "icemaker" reducer (available anywhere plumbing dept).
Middle photo: Easy-peasy DIY sensor exploded view. Sensor tubing available at brewers' supply shops everywhere for $1 and up. Measure, solder, fit, insulate, assemble, done. Make custom sensors you just can't buy (at least not under $40).
Bottom photo: How the TO-92 sensors fit in icemaker tubing, 1/4" OD. If you buy straight sections, the sensor will slide right in. Coiled tubing not so well. Cheaper than stainless and easier to solder or braze for permanent mounting. Will slide inside a 1/4" copper or steel pipe plumbed as a thermowell.