[Drakker]

Well, first, high ROF is most often than not a disadvantage, especially in limited ammo scenario. Also, some (very few) avenues, mostly CQB places, have limits on ROF. But if you still want it, you have two choices. Try to find a Tokyo Marui High-Cycle series AEG, such as their short AUG or their MP5K which do around 25 rps with a standard NIMH battery. They shot around 270 fps, but still have great range. The other option is to find any AEG with room for a large battery and use the most powerful battery you can find this should give you between 20 and 30 rps. You might also have to change the motor to a high-speed motor in some of them, which would help reach 25-30 rps. A weaker spring will always help improve cycling rate, so a power downgrade should be considered.

G&G is supposed to put an AEG with a dual sector gear on the market soon. Its a special gear that pulls the piston twice in one rotation. It means it has no semi auto option, just two rounds burst and full auto. Normally you can reach incredibly high ROF with dual sector gears, but somehow, G&G managed only 30 rps and claims it is very high.

If you go high-ROF, be prepared to have lower power. High power springs and fast cycling don't go well together. Anyway, a very high ROF gun at high FPS would be incredibly dangerous, especially to your teammates in case of an accidental friendly fire at close range.