27.550 was reserved for Federal use last time I checked the FCC website. There are only 6 channels legally available for use in the 27MHz band for RC in the US (and I believe Canada adapted those regs as well)</p>

Vendors may sell those crystals, but they aren't legally responsible if you use them - the FCC do not allow you to replace the Tx Crystal as far as I understand their regs - you must have all transmitter modifications carried out by a FCC licenced radio tech.</p>

Something to keep in mind before you get caught jamming up CB radio channels, and get fined $$$$$....</p>