From the Constitution (Article II)

Section 1. This organization ... shall consist of not more than fifty-five members, who shall be residents of Mercer, Burlington and Hunterdon Counties in New Jersey, and Bucks County, Pennsylvania.

Section 2: If at any time the number of regular members is less than fifty-five, additions to the roll may be admitted only as follows:

Any member may propose an individual for membership by obtaining from the Secretary a membership application form and returning it, filled in, to the Secretary. This application form will be promptly submitted to the Membership Committee, who will study the suitability of the proposed individual. If the Membership Committee approves the application, the proposer shall be so advised and, at the next meeting, he will nominate the individual for membership. A ballot shall be taken, and if not more than one adverse vote appears, it shall be the duty of the Secretary to invite the person to become a member, subject to his acceptance in writing.

(1) Get to know a member.
(2) Ask him to invite you to attend a meeting as a guest.
(3) If you like what you see, ask him to propose you as a member.
(4) If all goes well, welcome to the group!