buy 'Broadcast' magazine which contains details of any and all vacancies within various TV companies and the contact details of their HR departments. Send your CV in to them explaining that you would like a job in TV/ radio whatever.
A word of warning - you will almost definitely have to start at the bottom as a runner/teaboy or teagirl and put up with very low wages for a fair amount of time at the beginning. Everyone has to do this. Then its a matter of making a good impression, meeting the right people, networking successfully, getting your face and name known to people in lofty positions so that when the time comes to apply for a better position, they'll say "ah yes, Becks - she's a cracking wee worker, always on time, never complains, makes a fine cup of tea" etc. etc. and away you go. Good luck.