The association is probably formed as a nonprofit mutual benefit corporation. The association owns the copyright of all of its forms, and it can control who can and cannot obtain copies of the forms and under what conditions.
It seems to me (as I'm sure it does to you), absurd to make it more difficult for members to obtain real estate forms than the general public. However, if the Arizona association of realtors is similar to California, where I practice, then I would assume that you pay less than a member of the general pubic does for the forms.
Also, in California, we are given a free subscription to Zipforms as part of our association membership. This makes the forms and any updates free, and it allows a realtor to fill-in-the-blanks and print any form at any time from their computer at will. I can't frankly think of any real estate agent who still uses the multipart forms to write an offer or listing agreement -- because Zipforms is so much less costly and more efficient.
Anyway, back your direct question, a copyright holder can absolutely control to whom copies of a creative work may be distributed and under what conditions. 17 U.S.C. 106
So, if your association wants to make it difficult for you to use the forms, then it can do so, and your only recourse is to comply, or use some other form -- or, try and have the board of directors of the association removed and replaced with a board that is more accommodating to members.
I'm sure that you cannot be the only person who has a problem with this issue. With political matters, such as this one, it's votes that count.
Hope this helps.