Oops, forgot about the OP.

Does the thing have three wires or two ? What's more some of these have special mounting and all that. What's needed is a picture. It's possible Digikey has something, but not very probable.

There are places on the net that carry parts for these things, however if it is not defective and you just want to change the "parameters" so to speak, that's a different story. Maybe if it is just a rheostat (two wires) the range can be changed by just changuing the resistive element. This is not all that likely.

To change the range, it's better to look for a series resistor off the rheostat and just change that to a lower value. If it is being used as a pot it is a little bit trickier, but can be done.

We need the wires counted and a picture, plus a full model number so that maybe there is a print or something on the net.

J