Recently My 73 yr old Dad handed me down a Remington 592M 5mm, s/n 1118848:) . Unfortunately I'm missing the rear sight rib and rear sight assembly. 'I'm happy to say that's the only problem I have with this jewel of a fire arm'. I'm guessing that they were removed to make clearance for a scope mount job . Obviously since I'm on here asking for help to find a replacement that I've already asked my dad. Looking at the instruction folder and parts list for this rifle, dated 1970, "Remington/Dupont" the price for replacements add up to a grand total of $3.50. 'Those were the days'.
Thanks for the tip, I actually have an account with Gunbroker.com and found the item you pointed out. I'm thinking of purchasing a second 591 or 592 for parts instead if I can find one that's in a less then desirable condition for a couple of hundred $.