Originally Posted by FRC 2005 Manual, SECTION 5 THE ROBOT
<R90> There is no limit to the number of solenoid valves, air cylinders, pressure regulators, and connecting fittings you may use on your robot. They must, however, be “off the shelf” pneumatic devices rated by their manufacturers for pressure of at least 125psi. Besides the “free” pneumatic components listed on the Pneumatic Components Order form, you may purchase additional air cylinders or rotary actuators, however, they must be identical to those listed on the Pneumatic Components Order form , and obtained from a Bimba or Parker Hannifan distributor.
Please refer to the highlighted parts, pretty much its all ready in plain english right there. If the cylinder you want to use is on the pneumatics order form (last page of the 2005 FRC Pneumatics manual) then you can buy it and use it, if its nto there, its not legal to use.