I've heard about theses things but have no idea how you can find them
How often do they occur? Always wanted to check one ou

...the drop down of the "TER General Boards" at the top left of the page.

Meet & Greets used to occur more frequently when Bond007 was the host.  Now they are run by a group of providers who put them on in various cities.  The last one in L.A. was in October.  The next one scheduled for L.A. is April 17.  You can follow the details here as they become available:

http://www.lamng.net

Thanks