You might also cruse what the FSU has to offer, especially The Ukraine, in the way of filters and push on adapters.
I have a small number of filters, the basic FSU b&w colour contrast family, and some have push on rims and others, Kodak, Zeiss, etc for 'Series' VI plus threadless glass.
Many here will hate this piece of advice, but you can also cut gel filters to fit plastic caps that snug up to the Zeiss camera rim lens.
For that matter, if you want to try your hand at a little light metal work, thin brass, bronze, copper or aluminum sheets, most commonly available from K&S Precision Metals, can be cut and formed into a push on rimed gel holder, with a touch of silver soldering and a burnished over rim for holding gels.
In the copper and brasses, which include bronzes, I suggest 24-26 gage metal, though K&S offers phosphorus bronze in one sheet form, which is 6" x 12" and quite thin, spring material.
Whatever you decide, if you like how it performs, go for it.
By the way, I did no offer up glue/epoxy as an option for making a metal rim, as some will outgas, such as super-glues and fog/film your optic.
Rivets will mark your lens rim and possibly, your gels.
Cheers and Godspeed to All,
Eli