Exactly what crystal do you need?
Channel 40 is 72.590 mhz. I searched Horizon for 72.590 under JR radio parts
http://searchrc.horizonhobby.com/ind...demandrank%7c1
They have 4 items listed as available to order
FM Receiver Crystal
FM Crystal Set
FM Transmitter Crystal
FM Dual Conversion Receiver Crystal

To answer the question about using a Spektrum module in your transmitter, you need to list the exact transmitter that you have.
If the transmitter has a large removeable frequency module in the back, you probably can do it.
If it has a regular crystal in the back, or front, you cannot use a Spektrum module in it.