>perl -MDBI -le "print($INC{'DBI.pm'});"
r:/Utils/perl/site/lib/DBI.pm
[download]

That's how you find the path to a module that's already been used. I'm not sure if it answers your question, however, especially since you're talking about packages. Packages are not associated with any file. Mutiple files can use the same package statement, and it's possible to add vars and subs to a package without using the package statement.