Proceedings volumes can be purchased online via the Nebraska Maps and More marketplace.
To visit that site and see all available volumes (both hard copy and CD-ROM), click here.
Available volumes are as follows:
12th Proceedings (1986 - San Diego) Out of Print
11th Proceedings (1984 - Sacramento) Out of Print
8th Proceedings (1974 - Anaheim) Out of Print
1st through 4th Proceedings Out of Print