Many of these do not belong to the National or California Association of Realtors, many are part-time and some have their license's on ice.
I am in CA also, so my number will be the same as PAMs (thanks PAM).
When I was new, I used to worry about the ratio fo Realtors to Households, then I found out the industry weeds out many. Just like any other profession, the good ones produce and the bad (or weak) ones gradually disappears.
I don't think there is a underservered area anywhere in Marin, CA.