Here's a Zeiss 21mm finder.

Made in the 50's and early 60's for both the Contax and Contarex versions of the Biogon 4.5/21mm.

Clean condition, with just a few signs of light use.

Clean optics, just a slight haze.

Please have a look at my other auctions for more items, - I'd happily combine shipping costs.
Good luck!