How can I increase inductive spike voltage?
In fact the voltage at the drain of the MOSFET will begin to &quot;ring&quot; at the resonant frequency of the capacitance and the inductance. The capacitance comes from the MOSFET drain capacitance in parallel with the distributed capacitance of the coil.
The peak will be higher if the capacitance is lower, the on time is very brief and the resulting current peak very high.
In practice, a boost of more than 10:1 or 20:1 is difficult to achieve (and unsupported by most controller chips- the 'on' time becomes very brief), so a transformer (or tapped inductor) makes more sense than  trying to use your circuit.

Or, if you want to avoid using that kind of inductive component, you can use two stages to easily get higher ratios.