Where can I get free authentic listing for casting calls (without getting scammed)?

The best way to avoid getting scammed is to research and learn the business end of things including the casting process. Companies are not looking to pull people off the street and put them in a movie. Casting directors are not interested in going through thousands of unqualified submissions which is why they prefer to go through agents to find qualified actors. Casting directors generally provide breakdowns for mainstream movies and TV shows only to licensed talent agents and not the general public - and agents/agencies actually pay big bucks to access them.

There are websites that list casting calls - Actors Access, Backstage, Casting Networks and others. Most of the listing will be for low-to-no pay jobs in things like student films. They do charge a fee - some provide listings for free but you have to pay to submit to the call so charge a membership fee. They are providing a service - so it makes sense that they be compensated for that. Actors do make investments in their career.

By getting signed with a good agency.

They don't advertise real auditions for professional work in public any more - everything goes through agents.

When your resume/CV is really excellent, packed with details of your high-level training and loads of experience, approach agents, as your drama school will explain.

Look up local agency's around you that are legit!

probably nowhere for free