No worries, it's under the About Us on the RA-AUS website, although it's hardly user friendly website.
If such a letter was a submission regarding a board discussion or resolution (i.e. change of policy), then I wouldn't expect it to be remain private but included in the brief on the discussion. If the letter was just bitching about someone on the board or office then I would consider it more confidential. Keep in mind the constitution gives any member the right to attend the RA-AUS HQ and read any document or paperwork held by the association, to me this would include emails. Why we couldn't make life easier for the members and just publish relevent documents to the membership, but then I wonder if more members knew what was actually going on maybe more would get involved, doubt the Board wants that.