Budi Rahardjo has also made some examples and documents available on the University of Manitoba's Electrical Engineering department's FTP server. Budi also suggested sites for several publications and software distribution.
According to Brent Welch, author of the book Practical Programming in Tcl and Tk, soon to be published by Prentice Hall, several sites provide Tk/Tcl information or software. Here are some sites you might want to try (we can't vouch for these):
Incidentally, Welch's book is a good way to learn Tk and Tcl, and his practical approach might even give experienced users some good ideas. Of course, the definitive text on Tk and Tcl is Tcl and the Tk Toolkit by John K. Ousterhout, published by Addison-Wesley Publishing Company, Inc. (ISBN 0-201-63337-X).