Where can you find the rear peep sight for a Stevens model 56?
Try Bob's Gun Shop... http://www.gun-parts.com/savagerifle/
I have not orderded any parts yet from them, but they seem to have quite a selection of parts for the savage and springfield Stevens rifles. I recently was handed a model 56 less the peep site, buck horn and 5 round clip. The gun's not worth much, but it seems like a fun project.
I have one of the Western Field 38 and after some searching on the internet I found a sight with OLD mossberg catalogs on it. http://home.epix.net/~damguy/catalog.htm it looks like mine is a Mossberg Model 35 with No.3 Peep Sight and and the mulit post ramp sight. I think the No.3 peep was a lower cost option than the micro-click. Mossberg did in fact make that rifle for Montgomery Wards.