I'd drill and tap for a rear sight. Competent gunsmith should be able to do quickly and cheaply. Plenty of options that won't require a rail but will require a screw. If that was the route you wanted to go I'd just buy the rear sight first and take it to them. If I didn't want to do that, and some folks might blast me for this, but as low priced as those guns are I'd likely just JB weld a a rear sight onto it and disregard the screw.
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