try armstrong method of Indirect FM transmission

or try to read book communication electronics by freznal , you may find some designs in it for FM generation

Use basic FET reactant Modulator across any oscillator. it will increase the frequency of oscillation, we obtain FM wave using FET Reactance modulator.

there are so many oscillator available, as near to your question my suggestion is to try voltage-controlled oscillator (VCO) with integrated varactor (a.k.a. varicap diode)

If you want temperature and supply-voltage stability, I recommend going for a crystal-locked oscillator. Do a google search for "crystal locked fm bug" and you'll find lots of low-power transmitter circuits. The basic concept is you have a crystal oscillator at (say) 15 MHz and use a series of tuned (Class C) amplifiers to multiply the frequency to where you want it. Modulation is achieved by perturbing the crystal's resonant frequency (the crystal can be modelled as an extremely high Q RLC circuit, so a varactor can also be used to perturb its resonant frequency).

Another alternative is to do your modulation in software and directly generate an IF signal, then again use a frequency multiplier circuit... you can mix that with a numerically-controlled oscillator (and filter/amplify as needed) to upconvert to the desired RF. There are plenty of cheap SDR boards which can do all the necessary DAC/mixing/NCO stuff quite cheaply (you implement most of the radio in C++/python or Matlab on a host PC).