Pre-built binaries for specific versions of [Solaris] are available at
http://sunfreeware.com/ -- be absolutely sure to get a version for 
your ''exact'' version of Solaris, as a gcc installation is very
tightly coupled to the Solaris header files, which tend to "evolve"
between OS versions.  Any of the [gcc] binaries at this site may be 
used to build [Tcl/Tk] and all of the [C]-based [extension]s.  A more 
recent version of gcc (such as 2.95.3) is suggested for [C++] extensions,
which one would build from source using an older gcc binary.

Also, [ActiveTcl].

Also, [Tclkit].

Also, "tclsh is /usr/sfw/bin/tclsh8.4 in s10_72 ... [[and]]
Tk is included with Solaris and has been for quite some time
in package SUNWTk", Dave Uhring helpfully points out in regard
to "the optional software distribution".