From your post, you can rule out factory sights. The factory rear sight resembled a banjo and the slide was milled to accept it. The front sight was machined as part of the slide IIRC.
Other replacements are going to depend upon exactly what machining was done to the slide to fit the rear sight. You can always shorten the front sight to match the rear. Or, a dovetail can be machined in to accept a dovetal front sight.
The primary makers of adjustable pistol sights were Bo-Mar and Millet. Bo-Mar is out of business, but there are duplicates by other manufacturers. They had one model with a unique dovetail, if your slide is machined for that, you're in the position of going to a gunsmith and having a sight custom made. Millet may still be in business, check their catalog/website to see if you see something that matches.
Come to think of it, S&W made an adjustable sight that may have been retrofitted, it featured really big ears to protect the sight. Check S&W catalogs or parts lists for maybe 10 years ago.