After extensive research, I have uncovered the following:
At least four (almost certainly not more) examinations have been released. The numbers are as follows:
GR9768 (the free and only easily accessible one).
GR8767 available in Practicing to take the GRE (1st Edition)
GR9367 ditto (2nd Edition)
GR9767 (3rd edition)
I currently own the first and second editions but am unable to find the third edition at a reasonable price. The seller informed me that it contained 9767 but i was unable to confirm. (NOTE: i was careful that it was indeed 9767 and not a typo meant to be 9768).
A few additional points: the second edition of "Practicing to Take the Mathematics Test", in addition to the practice test comes with 63 practice questions and answers. These were nearly all (if not all) taken from 8767. Therefore, if you have the second edition there is little point in buying the first since there is a huge overlap.
The third edition contains 9367 and 9767, so again, only one new test if you possess the second edition.
I also have the "Mathematics Test descriptive booklet" from 1993-1995, published by the ETS which contains 36 additional sample questions. As far as I know, these questions do not appear in any of the editions of "Practicing to Take the Mathematics Test".
Anyway, the difficulty in acquiring any of these is considerable. Surprisingly, the most difficult by far is the third edition of which I have only been able to find one copy for sale and at an exorbitant price. If anyone has a copy and would like to trade for another edition, please let me know. Unfortunately, I don't believe it is possible to legally scan and post these rare materials, or our lives would be much easier.
Feel free to contact me if any more questions. As hinted above, however, i will not engage in illegal behavior no matter how much I am begged. If anyone knows legal information, PLEASE LET ME KNOW!
One more comment: There is an old preparation book that i have not seen mentioned on this forum, or anywhere else on the internet. It is called "Mathematics: Advanced Test" by Morris Bramson. Actually, there are a number of editions all with slighly varying names. Another is "Mathematics: Subject Test/Advanced (Graduate Record Examination). All editions are out of print, and very diffucult to acquire, but i was able to order an old one that has not yet arrived. I'm not sure if it contains a review, but i know it has practice questions. The lone review on amazon.com states:
"This is a comprehensive collection of samples of GRE MATH SUBJECT TESTS that I've found to be extremely useful, most approximate to the real tests! You will see! Just wonder why they are not publishing it anymore!"
Wow if it's anything like the reviewer said, it should be a fantastic resource ! I will write a review on this site as soon as the book arrives.