A spring returned spool valve? You mean like an automag, which is a spring returned unbalanced spool valve (ions are air returned unbalanced spool valves, matrix are balanced spool valves). Yeah, it's been done, and mass produced.
This is a signature?
EDIT: For some reason selling O-rings in the Misc section isn't allowed. This is stupid. PM me if you want to buy an inexpensive set of O-rings for your DM* marker.