My camera club designed and had made a collapsible metal frame for displaying prints. The local governing body specifies print mounts to be 500mm by 400mm, and I seem to recall it can hold around twenty of those.
Typically, it is used in competitions to display the prints that the judge has "held back" for fur the comment.
Unfortunately the club doesn't meet during the summer months (we are supposed to be out taking photos) so I can't take a picture, but if it sounds interesting I expect I can get more details.
We are based in Cheshire, in the UK
Dave