As mentioned, Steele Rubber Co. I had a pair of 1960 GMC V6 motor mounts revulcanized by them for $100. These were very basic rectangular rubber blocks onto a flat plate, so depending on what yours look like will determine cost. Many times there are other mounts, for something else, that can work. Is the mount just a bushing and washer stackup? If we see a pic of yours we can eliminate a bunch of false leads.
Several sites show the 3 hole mount for 235. I guess that is the side mount. Can you switch to side mount? Is 1960 different from 1961 and up 235 mounts? Have you checked 55-59? Anything
here?Most of the time an old part number does not do any good anymore. You have to dig the internet.