How to show organization interest?

Basically I want to become a member of XYZ organizations grad chapter. I would have tried undergrad but never really had the G.P.A., and I had mixed feelings with members who just sport the letters, but are nowhere to be found when its time to work. I realize now that its the person that decides on how they will represent the organization. Anyways how do I show the organization that I have interest in becoming a member? I don't know any members in the grad chapter. I know some members who went through the undergraduate process, but I don't know how to approach them with my inquiries. Also at the university I attend I only notice programs for the organziations undergraduate chapter being posted, but nothing refering to grad. So if anyone has serious advice let me know something

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