You usually don't have to apply yourself, it is often done by the people that organise the film festivals themselves, as they pick from the thousands of films submitted - Just because you put yours in doesn't mean it will be shown of course. Then if it is a well organised festival, they will get the classification exemption. I am a registered classification agent and can classify games and short films, and I often fill this role, or get the required exemptions at festivals/showings etc.

You don't really have to wait for anyone else to get the script written, or at least the treatment. Make sure you register you stuff with a writers guild or similar - it protects you, and is a really good idea.