tclconfig is found in the tclconfig fossil repository at http://core.tcl.tk/tclconfig . It contains some TEA specific files which typically reside in the tclconfig subdirectory of a Tcl extension. Copy them into that directory if you need to create an extension with autoconf.
Note that this directory (in the file tcl.m4) provides for the extraction of information from tclConfig.sh (installed with Tcl itself) for the use of the TEA directory that it is embedded in.old tclconfig description when Tcl was still maintained on sourceforge
The contents of this directory can be found in the sampleextension module that is a part of http://tcl.sf.net/ . It contains some TEA specific files.