They are out there, but they are truly rare.
Many LE agencies had no use for the rail on a handgun and ordered TSW's from S&W sans rail.
There were a bunch of 5903TSW's from Atlanta PD, and Gwinette County Sheriff too IIRC, that were made without the rail and no holes in the dustcover.
It took me several years of searching to track down a full size 4513TSW without the stupid rail. Well worth the search. I'm currently looking for a 4566TSW made without the rail.
I would advise against "mixing and matching" TSW top ends and frames. The frame and slide of S&W TSW series pistols are matched and fitted at the factory. Both the slide and frame bear inscribed numbers so that they could be kept together during assembly. This was done to guarantee function, accuracy and reliability. Seperating them would not be a good idea, IMO. Good luck with the search! Regards 18DAI