Well, expr is almost the only external that is delivered *with* Pd. It should be in /usr/lib/pd/extra/ or similar.
kind of had a feeling that was the case, is anyone opposed to putting bonk~ fiddle~ expr~ etc into the externals build system? in my case i just did a checkout -r devel pd/src long ago...and had removed the extra stuff from the makefile anyways due rebuilding those every time on 'make clean'...i mean if someone thought it was good enough to include in the default pd distribution...its surely good enough to include in the externals distribution as well, no?