How to get a high precision sine wave not available from standard crystal?
How to get a high precision sine wave not available from standard
  crystal?


Inevitably, when transmitting power across a gap to an RFID device, to obtain best efficiency it is likely that you will make the transmit coil resonant (using a tuning capacitor) and similarly, you will make the RFID coil resonant also using a tuning capacitor.

The effect of "tuning" means that if you fed a square wave to the drive coil it would largely transmit a sine wave so, the process of producing a magnetic field will convert your square wave into a sine wave. There may be some other reasons to use extra filtering to improve the sine purity of course.

So, if you can make a square wave oscillator that runs at 27.095 MHz then your coil and tuning capacitor design should produce a reasonable sine wave. How pure this sine wave must be is down to you.