ChrisD,
Carmen Axtell still sells some misc. sight parts on ebay under the username "carmenda". Although I have never seen eyecups on her auctions, you could send her a question via one of her auctions asking about the thread pitch of her sights.
if you cannot find her by searching her user name, search "tang sight" and you will find some of her auctions.
Good luck with your search.
Chris
