01You already know a member
Ask them. If they think you belong here, they put your name forward at a meeting and the group takes it from there. This is the route the whole thing is built around, and it is by far the fastest.
One seat is currently held. If you know that person, start there.
02You do not know anyone yet
The directory is public for exactly this reason. Find the seat whose clients overlap most with yours — your CPA's clients are usually your clients too — and contact that person directly. Their direct line and direct email are on their page.
Make your case to them, not to us. If you convince them, they carry you in. If you do not, that is useful information about the fit.