I don't know if 5687 are still made, but there are tube manufacturers, Shuagang and Linlai in China, JJ Electronic in Slovak Republic, and Reflektor Corporation

I don't know if 5687 are still made, but there are tube manufacturers, Shuagang and Linlai in China, JJ Electronic in Slovak Republic, and Reflektor Corporation in Russia.[1][2] But 5687 are not rare.[3] [1] https://www.thegearpage.net/board/index.php?threads/current-tube-manufacturers-list.1740893/ https://www.thegearpage.net/board/index.php?threads/current-... [2] https://linlaiglobal.com/ https://linlaiglobal.com/ [3] https://www.ebay.com/sch/i.html?_from=R40&_nkw=5687 https://www.ebay.com/sch/i.html?_from=R40&_nkw=5687