How to find a producer for a feature film script
Right, firstly, stop just writing to them enclosing the whole script.
Film is visual, ok - obvious? It's surprising the number of folk who write to production companies enclosing what they think is the greatest script for a feature since Gone With The Wind and can't understand why they get no reply or a holding reply and then a "no thanks".
You need to make a trailer. What - how can I afford to do that you cry? Well you jolly well need to.
Set up a really good website. You can advertise for a cast, choose the best scenes from your full length feature and just put it straight to the actors: ok, this is an unpaid trailer to secure a big screen feature film - can't pay you now but if you commit to this project and give me your best work then if I am successful in securing funding then you will be allowed to reprise the role and play it and get paid.
Then you need stunning photos. Don't just have a Facebook site - on that proper website you've got (beg and borrow a designer if you haven't got one) paste up fantastic stills showing the characters.
Now you need to enlist make up artist(s) and get great costumes (make up artists will do it for nothing in return for absolutely stunning photos that they are allowed to use on their website).
You need the best sound men and camera crew and you may need to fork out money for this - fish around and see what you can get for free with promise of future paid work if successful in gaining funding.
Don't do an amateur/student film job on your trailer. Do it so folk will mistake it for a Hollywood standard film trailer.
Now you've actually got something other than a script to show a potential investor.
Send a synopsis along with the full script (make 100% sure you've put your copyright symbol on the script/trailer) to your proposed investor.
British Film Council is one possible option to approach - but what about your local city council arts department?
Ask what incentives you could offer a potential investor - can you offer your local council, for example, the promise to use young unemployed folk in part of your film? Could you use disabled folk? You will need to expand on the few numbers of folk you've used in your short trailer so you'll have a lot more casting to do anyway - why shouldn't a certain number of your cast be from a particular section of society - one that will attract a local council to back you.
Check out National Lottery funding.
Why not run some articles in the local press about your trailer to try and gain publicity/funding.
To actually get that person to agree to produce it - why not advertise on CCP newsletter (I had a play I had written performed in London in this way).
Even try places like London Gumtree try websites for film crews.
Don't know if this is helpful or not - I do know from personal experience though that having a proper professional trailer of your proposed full length film will enhance your chances.
After that - I suspect it's a case of internet marketing - put that trailer and synopsis in front of the right folk and use websites for crew/production teams.
Best wishes - I am currently involved in a feature film that started off with a trailer.