salt-run winrepo.update_git_repos
And then update the database on your minion by running
salt * pkg.refresh_db
If you've done all this already, then you may need to do some further investigation into the software definition file itself.
These are stored on the master at
/srv/salt/win/repo-ng
All files in this directory and sub directories are synced down to the minion and used to refresh the database. The .also file for the software you're trying to install will be in one of these directories. You'll want to look at the 'installer' value and make sure that the URL is accessible from the minion.
If your still having problems, please post the name of the package you're trying to install along with it's sls file.