I'd say that you would benefit from reading the Concepts book (find it on the Documentation page). Why? Because - unless I'm very wrong - it is not a "database file" you are looking for, but a "sample schema".
Oracle databases already contains sample schema(s); the legendary one is Scott's schema (user name is SCOTT). Or, you might search for the HR schema, which *might* be locked so - perhaps there's no need to search for it - it would be enough to simply unlock that schema.
Oh, yes - a huge schema? I don't know anything about it. The ones I have mentioned are quite small.