All available from Grainger(reg.) or Landis & Gyr(reg.) BUT, SHOP AROUND prices vary GREATLY!
Must use dry, regulated (<30 psi) air but can make logical gates and operate higher pressure pneumatic valves ($94) same suppliers
Your throttle assembly might consist of: A pnuematic positioning switch($40) strung to your MOTORCYCLE twist grip!
Then the output from that would control a pneumatic valve($94) which has a 1/2" output!