The automatics come with either fixed or military shrouded adjustable sights. THe slots are a tapered broach method.
It does not make sense to try to replace the slide-upper part-
I found a set of adjustable sights for my 5906, through I think Midway. THe company that made the adjustable sight is
LPA sights
Produzione mirini, tacche di mira e accessori per pistole semiautomatiche , revolver e fucili
They go into the gun from Left to right-gun bbl facing away from you-since it is a Tapered dove tail. Under the sight-in the slide top- there are two springs- make sure that you keep them contained, when removing the old sight.and they are different so put them back in the same hole...
I believe the company is european and makes sights for several arms manufacturers.
Good Luck.
THe standard S&W Military shrouded sight on a wonder nine makes the gun worth at least $100.00 more in value and it is shrouded on the end for protection...