There are 37mm push-on filters (and lens hoods) the problem seems to be that they fit some very highly collectable cameras, like the Voigtländer Bessa II, and tend to go for alarming prices, especially if they are the matching brand. I have slowly accumulated some (for my Ercona II), but in the meantime, as JLMoore3rd suggests, I found a push-on Series VI adapter and got some Series VI filters. Even they aren't all that common, the transition from series to custom dimensioned filters must have happened longer ago than I realized.