I talked to Ram Mount this morning and they did not even know what a 52mm or 2-1/16 gauge was. They said I was the first person who ever asked about a mount that would hold one. They directed me to a couple of part numbers,
RAM-231Z-2U and
RAP-401U. Does not look like either of those would work though. Basically their message seemed to be that they could not possibly make holders for every obscure device in the world and because they had never been asked about a round gauge before, I must be the only one interested in one. Kind of odd given how common round gauges are.