Like many of the people here they really don't want to get into trouble but on occasion wouldnt mind meeting up with new people.
So, have you (the core group here) ever tried either of the following:
Making a list of LEGAL but interesting places to go explore that would allow you to
a. do meet and greets with new blood without wondering who they are...
b. give new blood access with out the secret handshake (or cool places) and encourage them to stay active.
Just an idea...