Al:
McMaster sells spring loaded air cylinders. See:
http://www.mcmaster.com/#pneumatic-cylinders/=5dun1p
The single acting, spring-loaded cylinders look to me to meet all of the pneumatic rules this year (assuming the bore and stroke are within the limits in the manual, and the cylinder is rated for sufficient pressure).
In my opinion, the main advantage of these cylinders (besides simplicity and one less air connection) is that you are guaranteed that they will return to a known position in the event of an air loss event. In the case of a two-speed, air-powered, dog-shifted transmission, this means that you will always be in gear even if you lose air pressure.