Good luck with that. I know there are some people that keep those. Mine date back to 2000 and I have a couple of early 90's originals. I just recently read ALL of them AGAIN and I don't think I could part with them.
Have you called the GSCA to see what they have? I know they keep a good back-log of X-tras, prolly not dating back too far.
If you know someone who is a long time member it may be better to get them to request back issues.