The most venerable collection of Tékumel information and publications long resided at The Blue Room, an ftp site hosted by Chris Davis, who also hosted the excellent Blue Room Mailing List. Professor Barker was a regular contributor to the list.
While The Blue Room and its list are currently no more, almost everything that was on the site is now being hosted on Tékumel.com.
Some of the publications originally hosted by the Blue Room are now reformatted and offered for purchase at DriveThruRPG.com in addition to the new RPG system and the original EPT and maps.
In addition, a project to reformat and present all the 1,000-odd mailing list postings is currently in progress. In the meantime, you can download or view the original text files on the List Archive page, or search through all the posts using The Blue Room Search Engine.
Finally, a debt of gratitute to Chris Davis for all his hard work creating and maintaining The Blue Room and supporting the Tékumel online community.