Having tried all over the place, I finally got an answer back from a mask museum in the USA who said: 'What a great question. I had a long conversation about your question with our International Artist-in-Residence who is Russian. He said that a Russian word that comes close is maskovedening which means "knowledge of masks" or "knowing about masks". That term does not, however, refer to the collecting of masks, but, simply having knowledge about them. We'll keep searching for you.' So that's a start.