1. Magazines. There were many. Now almost none. One of these magazines I started myself, the TAM Bulletin. It run for several years and also was available in digital format.
See also: http://www.iuoma.org/tambulhi.html
2. Pass and add on projects. Each mail-artists adds his art and address and passes this on. That way the amount of address cumulates and is circulated. When someone makes a few copies of such a paper and distributes. It speeds up things even more
3. Addresslist that were used by the older generations were published in catalogues.
4. The Xerox machine helps to distribute information. Nowadays people just copy and paste. (And e-mail to a large senderlist)
5. Network is a lot of work. Distribution costed more energy and postage....... Some projects were meant to expand the network. I did a socio-project which even run out of hand. I asked 25 people to copy a 'controlled' chain-letter. Add your name and send it to howmany neames you want. Send me the namelist of the people who will receive the list. This expanded and brought me over 3000 addresses. To document such an event was very difficult. But I did try.
just a few ideas.....
another sample of early networking: one page out of the TAM-bulletin with some historic projects.