Jeb, Remington used both outside vendor rears and their own. The Remington Model 12A,B,C,Cs,D E and F made from 1909 to 1936 used: 1912 No. 28 frt and No. 173-1/2 rear...in 1919 it was the No. 28 frt and the No.98 1/2 rear...in 1923 seems like they cleaned house a bit as the frt remained at the No. 28 but you will find both of the rears used( 173 1/2 or No.98 1/2...that is the EZ part because they also used outside vendors for both the front and rear. Vendors included Lyman,Marble and King. The Lyman fr5ts: # ivory bead...#20 Ivory "JACK"....#28 "Semi-Jack"...#5 Combination frt...the #7 Windage Globe and the #17 Globe...MARBLE: Sheared gold bead....Reversible bead frt..... Standard frt....Improved frt...Duplex Frt...Vicker's-Maxim Frt...KING: triple bead frt.....Spark Point Gold bead and the Gold bead frt. These were matched to these rear sights: Lyman # 1 and # 2 Tang sight....Lyman #6 folding rear...Lyman #12 dovetail blank....Marble: Flexible rear tang...marble #95 folding rear leaf....KING: No. 10 Sporting rear leaf.....No.6 folding rear. The Model 12C N.R.A. Target Grade had a standard sight package of: Lyman #7 Windage Frt paired with aNo2 tang sight and an optional set-up of the same sights used on the Model 12A repeating rifle..Basically you have to know the vintage of your rifle and be able to ID the front sight to pair it with the proper rear the bad news is that some of the originals can sell for 3 figures........ However..I believe that an aftermarket replacement may be had thru Brownells. For the original..if GPC doesn't have it..then contaqct Gary Fellers...23 marie Lane, Ft Worth, TX 76123-2055 the last Ph# I have is (817)346-9633..gary is a good old boy and is more than willing to work with you.....