The present receiver will work with a Hitec,Fleet or Futaba transmitter.It will not work with a JR or Sanwa transmitter.For the transmitters,you need the correct supplier and frequency of crystal.
Rick,you can purchase a synthesised 40Mhz receiver for £15 from Giantcod or Ebay.They do not use crystals and usually work with both positive shift transmitters(Hitec,Futaba,Fleet) and negative shift (JR,Sanwa).
You can also get synthesised receivers with failsafe feature from Hitec.