There are a few modern games that come in both positional and hand-held light gun versions. Aliens Extermination and Armageddon are both this way. 43" screen versions (standard) have position guns, 55" screen versions (deluxe) have hand held guns. I'm not sure how much more 'nostalgia' you'd get out of having a fixed bug vs. a hand held submachine (MX24) gun. So the lines get blurry. If you've got a dedicated T2 or Operation Wolf cabinet, sure - go mounted guns. But if you're on a multi-cade setup, I don't see the benefit. I guess you could build a dedicated fixed gun cabinet... lol (MOAR CABINETS!)
There is a pump-action shotgun made with Sinden internals. Kind of neat. Its
really expensive though for what it is.
https://thunderstickstudio.com/products/grs-sinden-target-pro-arcade-lightgunThe only 'gun' game that I see being an issue is the silent scope games. Hard to fake / emulate that setup.
I tried using a real wii-mote as a light-gun a few times - and the accuracy / stability was horrible.
A side note: the RetroShooter MX24 sub-machine guns' recoil is LOUD. There is a mod to add a buffer on the solenoid to quiet it down. I'll be doing that to mine. You have to turn the game sounds up crazy loud so you can hear them over the constant full-auto solenoid recoil noises. (Maybe this forces more 'arcade experience' ? Every time I go into a modern arcade, it seems like every game has its volume cranked up to the max)