RX compatibility
#2
Recievers are proprietary, BUT you can use third party recievers, like Novak.
#3
Although, Airtronics equipment is also sold as Sanwa in some countries. Maybe look for that?
#4
Third party
Like Phat said you have the option of Novak, Sanwa and I believe Hitec makes a Positive shift receiver that will work with your Airtronics. Any of should get the job done.