I used to be on the board of directors of a
community theatre group. We were having difficulty finding new directors (still even a little
bit) and needed not to just keep using the same 4 or 5 directors over and over again (usually the same 3 really).
One of the directors started then "Directors Circle" (yes we know it sounds pretentious) a small group of people to talk about plays and directing and forming a core of mentorship to make directing less scary. Anyone in the community can join regardless of being a member of the
theatre group (but to direct of course you have to be a member, if for no other reason but insurance ones).
They put out adds and mentioned it during the pre-shot speal before every show the first season it existed.
First they got together to chat, get acquainted,
etc, and talk about some plays they might like to see done. This lead it's way to some informal workshops, and then finally "okay, you want to see that
play done, why don't you direct it? we'll be right here to help!". Now there are at least 5 more people who have directed in the last few years. Seems successful to me.