What's "real writers?"
Anyway, none. They don't go out there and scout. To me, "real writers" means professional writers. And to be a professional writer and be paid, one needs to earn it.
For movies the way it goes is, *production* companies either get writers from referrals, or agents and managers send their clients' work out. Professional writers have a body of work to show around, i.e. screenplays for movies and original pilots. The screenplays basically serve as writing samples to showcase the writer's skills, talent, knowledge of this craft and the biz, and their personal voice and style. If a producer likes the writing (and the stars align), they might buy the script or option it or, more likely, they will hire the writer to work on another project or even use another spec. Most of the time, though, the specs get professional writers assignments (for example, rewriting someone else's script for a producer). The more experience a writer has, the better his or her chances to land a good job or sell a script. Because experience means trust.
Another way is, a writer's work becomes highly successful in another field. For example, it becomes a best-selling novel. In this case, if this seems like a good business move (particularly, the franchise has a fan following, which means audience) a studio (or production company) might approach them or their agent to buy the rights to the IP in order to then (hire a screenwriter or screenwriters and then) adapt it into a feature screenplay.
As for TV, every show has a team of writers. The team is run by the showrunner(s), who hire the writers. Again, these are professional writers that either get to show their work and themselves through their connections or representation. But most of the time, writers start from a lower position, like a writer's assistant, and they climb their way up to staff writer.
Professional productions are not interested in random writers w/o experience and, most often than not, w/o representation and/or connections that can confirm the writer's talent and abilities, and especially w/o a body of professional work. They're not gonna waste their time sorting through writing samples by unknown strangers.