On amd64 10.2-release, using exlusively pkg I get this:
# pkg check -d taucs
Checking taucs: 100%
taucs has a missing dependency: metis4
>>> Missing package dependencies were detected.
>>> Found 1 issue(s) in the package database.
pkg: No packages available to install matching 'metis4' have been found in the repositories
>>> Summary of actions performed:
metis4 dependency failed to be fixed
>>> There are still missing dependencies.
>>> You are advised to try fixing them manually.
>>> Also make sure to check 'pkg updating' for known issues.
This works as indented: metis4 can't be redistributed so there's no package for it.