The sensor that I use, is also from Crouzet, its a 89750153 part #, here is a link http://www.crouzet-usa.com/catalog/_tempm2.shtml
I could not find them online, Newark Electroncis shows the wrong part when you put this number in.
What you want is a temperature transmitter that will give you a variable signal between 0 and 10V. Most industrial controls are 4-20 ma, or current loop, since that is more noise resistant in industrial environments. Current loop sensors can be converted to voltage by putting a resistor across the input, usually around 500 ohms.
Ebay is a good place to look, there are lots of used industrial electronics there.
Another option would be to use the Johnson controls analog controller, A350PS-2C, which is similar to the control that ships with the Harman VF3K boiler, the difference being that its output is a variable voltage as opposed to a contact closure. Both these sensors are in the $100+ price range.
Hope this helps