Actually that is a misconception. It would not make any sense to have Tx and Rx cystals "made from the same piece of quartz". Due to the way radios work Tx crystals and Rx crystals are very carefully made to resonate at DIFFERENT frequencies.

It is however a good idea to get your Tx and Rx crystals from the radio manufacturer so they are matched, i.e. made to the correct specification.

To answer the original question, if you buy a transmitter you can later buy a suitable receiver, but be aware that not all makes work together. The receiver does not have to be on the same channel as you can simply change the receiver crystal to match the transmitter (for any make other than Futaba). The rules for Futaba are a bit more complex. But you will not normally need to have anything retuned unless you want to change the *transmitter* channel.

Steve