The USB2GUN from America's Army does just this. It works with Windows and makes the Happ guns act as analog sticks.
The problem is they are very hard to come by. I have one and had it working in MAME with my Happ guns. There are 2 versions and the one with the JAMMA harness did not work but I came across the other one without it. I still have yet to actually put together the PC that I was going to put inside my Maximum Force cabinet though and make a dedicated light gun emulator cabinet.
Some of the games had issues with offscreen reload and I had a hell of a time actually getting it to work. But some games, specifically Invasion, was never solved to off screen reload and instead you have to offscreen reload twice. I googled forever and no one ever had a solution for this.
But in my current MAME cabinet I proof of concepted a few different emulators and ended up getting them all to work. Virtua Cop worked on the am2 emulator however since I'm on a standard res monitor, the text in it was not always readable. But the game itself was fine since everything was polygons. I got MAME to work no problem as well with the issue above for off screen reloading, and then I had the hacked version of Friction working as well, after going through like 4 different ones that didn't work.
Just the config alone made me not actually get motivated to actually put the PC together for my dedicated cabinet though. My plan was to sell off a bunch of boards I have and just run them on emulators but I never got around to it. I bought the PC parts like over a year ago and just never did it.
EDIT:
I also have the Friction conversion kit mentioned up above and while I believe I actually got it to interface with Windows, I could never figure it out and it definitely did not work as good as the USB2GUN board does.
Here are a few videos of it running. The crosshair you see on screen can be disabled I just hadn't done it at the time cause again, this was proof of concept.
This was before I got offscreen reloading working, and I honestly don't even know how I got it working but I know I did. I wrote notes down on that PC I was emulating on.
And oh here was my problem with Friction board. I could get the trigger to register but could never get the tracking to work.
Or maybe not lol, I eventually got it working somewhat but it never worked fully.