Andreas and Jeff try to keep pointers to such on the SourceForge release area (see [L1 ]).
ActiveState has pages for versions
KJN I have retrieved a number of old versions of Tcl 6.x and matching versions of Tk by FTP from old mirrors. Tarball is at [L5 ] (7.0Mb). The tarball contains these versions not available from SourceForge: Tcl 6.1 and 6.5; Tk 2.2, 2.3, and 3.0; and assorted patches. Also alleged DOS ports for Tcl 6.2 and 6.7.
The old Sprite distributions should have a very early Tcl. (Tcl and Tk were originally available by FTP from the hosts sprite.berkeley.edu and barkley.berkeley.edu; these hosts have long been disconnected. John Ousterhout's Sprite network operating system project [L6 ] ended several years ago.)
The oldest version at SourceForge is Tcl 2.1.
See also