Why do you need a sine wave?
A pulsed waveform should be good enough.
There are many ways of designing a 20MHz to 40MHz oscillator, I just posted the simplest method.
Change the values of C1 and L1 to alter the frequency. The value of C2 will also need changing if you change the frequency significantly.
If you need an accurate oscillator, use a crystal and a harmonic filter. Assuming you're using a microcontroller, it should be fairly easy to tap the clock, thus eliminating the need for a separate crystal oscillator.
EDIT:
Please post a schematic of your idea.