Email is the best (and fastest) way:
Our President wants to hear suggestions for events, gossip for the newsletter, gripes, and compliments: firstname.lastname@example.org
Our Membership Chair handles all membership questions (Did I pay my dues? Am I on the list?): email@example.com
Our Web Manager will field all Web-related issues at firstname.lastname@example.org
If you prefer paper mail, try writing to:
P.O. Box 19110
Washington DC 20036
Somebody collects mail from there, more or less regularly.