The One Ring (CZ Biotar)

I've been given a CZ Biotar in Exacta mount in pretty good conditions, which however is separated in its two main component (the lens assembly and the focus mount) because the aft ring that keeps them togethere is missing. Does anyone have any suggestion as to where a spare ring could be located (hopefully not in Mordor)? Alternatively, can a compatible ring be taken from other less valuable lenses? Thanks

PS: The whisker between the two elements is also missing, and thus I understand it would be nearly impossible to obtain infinity focus. Still, I would like to put the lens together.