Canon Fodder pretty much summed it up.
However, if you’re planning to go down the DIY route, you can change any marker that has the bolt visible into a "pump". These can be Egos, Timmys, Spyders etc. I've made an Ego one (for ****s and giggles), and it is 100% reversible.
Problem is though, they aren't actually true pump action as the rammer is reset automatically by the solenoid; all your doing when you pump is moving the bolt backwards to load a ball.
If you'd like a pictured tutorial/explanation just lmk.