Need a gas valve to switch and select outlet air flow from two inlets sources

That may be expensive in that it might be an uncommon valve. Perhaps it would be better to use two valves and 'Y' their outputs together. You may find a solenoid valve you can use in the automotive industry. An EVAP solenoid http://www.amazon.com/ACDelco-214-1685-VALVE-ASM-EVAP-BRACKET/dp/B0049BROCI is one that handles fumes of the fuel system. I recently discovered two valves on a vehicle that I was working on to have variable ports actuated via stepper motors. - Scotty