That file should be on your cd. I am using mdk 7.1, and the file is simply
tetex-blahblah.rpm. Do a 'ls *tetex*' to see all the tetex rpms. If for some
reason it really isn't on your cd, (and its not on the other cd either) then you
can go a couple of places. Lots of ftp sites mirror sunsite:
ftp://sunsite.unc.edu/pub/Linux/distributions/...
where you can find the latest mandrake, among lots of other distributions.
Otherwise, you can check this site, which I find helpful in a general way:
http://rpmfind.net/linux/RPM