The single best repository for Visual Language information is Margaret Burnett's Visual Language Research Bibliography. At one time, papers published in the proceedings of the International Symposium on Visual Languages were required to be submitted to this repository; unfortunately, it was determined that this wasn't consistent with IEEE policy so the coverage in recent years is less complete than formerly.
I have the proceedings of the Symposium for 1990-2000 and 2002 (in 2001 the symposium broadened its focus to become the Symposia on Human-Centric Computing, and I haven't been as regular an attendee).
I also have the proceedings for Diagrams 2002 and 2004, and for the Symposium on Distributed Multimedia Systems (which includes the International Conference on Visual Languages and Computing) for 2002 and 2003. In a week, I'll have the proceedings for 2004! week I'll have the proceedings
The campus library has reasonably complete coverage of IEEE and ACM conferences, and Springer-Verlag series. Coverage is better for material more than 5-6 years old (budget cuts combined with soaring journal costs...), and has a really great Inter-Library Loan setup. Also, it has a subscription to IEEE Xplore (complete on-line IEEE publications going back to 1988, and spotty coverage back to 1950) -- go to library.nmsu.edu, click on "Electronic Journals", go to "IEEE Electronic Library Online").