Choosing the values for this magnetostriction oscillator circuit
First look at the equation. You have Y,P and a desired range (upper bound) of length (l not L). It's trivial to convert that into a range of available frequencies with a lower bound, so do that first, and choose an achievable frequency ( &gt;= that lower bound).
If that is achievable (the lower bound encompasses the frequency range you want) you can compute an LC product from the LHS of the formula, and choose C such that L1 is in the microhenry to millihenry range for reasonable windings.
So far you haven't had to know anything about transistors.
But now you have to learn about common emitter stages and biasing networks, to turn that over-simplified sketch into a practical design. (Without base bias, there is no way for it to start!) That's a bit too big to tackle in a question; I recommend a book like Horowitz&amp;Hill or a college course in analog electronics.
(If the frequencies are really in the sub-MHz range you may find an opamp easier to work with)