If you are referring to the bolt, "all" of the K series are not interchangeable, and some minor fitting (of new ones) is usually required. Due to design modifications, there are some minor differences in the front leg and the thumbpiece stud over the years. There is however, no functional difference between the carbon and stainless components, so a correctly fit carbon steel bolt would work fine in your revolver if you cannot find a stainless one.
Numrich lists some used ones for the model 65:
Bolt (aka Cylinder Catch) | Gun Parts Corp.
If you continue to have problems finding one, let me know I have several new and used ones left from my armorer service.