Haven't seen that style on any original 1873 rifles....or others for that matter.......but for-sure that doesn't mean any existed.
However, there are some nice reproduction Winchester folding rear sights available...Dixie Gun Works used to carry a couple types & Smith Enterprises makes one - try Brownells for the Smith Enterprise sights.....
Of the bunch, I'd go with a repro Winchester or a Marbles for authenticity. The Smith Sight would be fine a fine choice for a big-bore long-range rifle...might be outta place on a saddle-gun.
Beech combo folding site is authentic, tho..seen those on 73's.
Slim