How to install a Tcl package?
Check this page: http://tcl.tk/man/tcl8.5/tutorial/Tcl31.html
Basically, to know where tcl looks, start a tclsh:
% puts $tcl_pkgPath
/usr/lib64 /usr/lib
% puts $auto_path
/usr/lib64/tcl8.6 /usr/lib64 /usr/lib
but note that you will also need to generate (or install, if you already have it) a pkgIndex.tcl (the same reference above tells you how to make one).
In CentOS, I just installed tcllib packages
sudo yum install tcllib