I don't find anything for Zayer, but I seem to remember a department store called that when I was a kid. Cross reference still doesn't show it as a store brand, so probably more info is needed. Pic would be helpful http://www.e-gunparts.com/crossref.asp
But most of the rear dovetails are similar in size, you could try one that's close. Should be an easy project for you or your gunsmith.