You silent people you....
I've now purchased a lot of plastic (poly) and will manufacture a stopper myself.
LOL, good job!!! I have no idea about the North stopper, but I also agree it can't be that hard to just make something.
I had a suggestion of a mod to the Naish stopper...if you cut a tiny bit out on the side and hook a line to the depower line the effect would be a stopper that cannot be moved unless you pull the line.
I made this mod on another bar. I could see if I can find it somewhere.