Tony Amor has 1 x 4AO-11515-00 Lab Seal (101 Seal)
I always go to http://www.boats.net/
and put the part number into the searcher at the top of the page. I have found they have pretty much the best prices, and if the part is still available, there is a good chance they have it, or can get it.
Trevor Otto in Adelaide, or thereabouts, may have a cache of TZ500J parts. He had a new one that Greg Pretty and Jeff Miller rode and was involved with the 2 J models we sold to the sidecar guys in Adelaide. Sorry, apart from looking him up in the White Pages, I don't know how to get hold of him.
Good luck with the hunt!!