I dont think you found any 2.4Ghz crystals anywhere, because 2.4GHz doesnt use crystals. Generally 72Mhz crystals are interchangeable between brands but I cant say for sure with Dynam.
Assuming you have a 2.4GHz transmitter it would probably work out cheaper and easier just to pick up a cheap 2.4Ghz receiver and swap the 72MHz receiver out. For instance you can pick up a Spektrum compatible DSM2 'Lemon brand' receiver for less the $6. I don't think you will find a set of crystals for that price.