I believe there is a way you can get the old perp weapons. They are called Source Weapons or something. If they are not made by XQ it would be hard to tell. Not sure how to get it tho as it was on my mate's server.
you can only get the models for the guns, they can be found if you look on the workshop hard enough, just scattered around places.
as for the scripts, unless you want to waste your time to try mimic the way they work by writing your own, dont even bother (tryhard af anyway if you do).
You can try to mimic the guns, but you would just be wasting your life. Just stick to just playing perp as it is and just get used to the guns by playing perp, the closest things could be found on the workshop.