Any spool valve that closes the dump chamber when the bolt is forward should work. That includes Ions (with dual-tail oring bolts), SFT and NXT Shockers (with HE bolt kits), DMs, Droids/Clones up to the Clone GT, etc.
And to convert them, all you need is a valve like this:
http://www.clippard.com/part/SMAV-3
And a bracket to mount it behind the trigger.