Uploading this for anyone else who is searching in the future. The EZ400 (green box, not the later grey box) used a 10K B3976 NTC thermistor probe from betatherm that is no longer available. Searching Digikey and Mouser doesn't show any exact matches, although some are 'close'. I'm not sure...
The problem is that there are a lot of different 'temp probes' thermistors, thermocouples and RTDs, plus newer '1 wire' digital sensors - and then mix in the fact that there are different sub types in each category, plus the plug type RJ9/RJ22 and its pretty hard to match something up without...