It seems that there is no way to use outlet collections in a mac application. Why not?
Just put your image views into an array -- if they're all subviews of the same superview, you can loop through that super view (testing for the fact that they're NSImageViews or checking a tag value) and add them. This way also has the advantage that you don't need to create IBOutlets for them.
Whether bindings are appropriate for your problem depends on what you want to do with the image views. I would need more information to comment on that.