I used to download them directly from Adobe, but it seems that a major refactoring of their site has broken nearly all links on all popular sites (TIFF - Wikipedia , TIFF File Format ) and even within the DNG-specification itself!
I hope someone is working on this.
In the meantime: Where can I find the current TIFF-specifications along with their supplements, tech notes, etc.?
The TIFF spec has been re-linked as is available on the Adobe site. https://www.adobe.io/open/standards/TIFF.html
The Supplements are now available, as well.
Thanks for the update.