Jonny,
A fair while since I did my work expereince, but I managed to get a fortnight at a local tower. The best thing to do is search out telephone numbers and stuff, even try dropping into your local airport and head to the info desk (they will more than likely point you in the right direction)
It took a lot of pre-planning to be able to get the space, so start work now! (I think i applied in September for the work experience the following May.. and i only just got it!). That's all I can offer really, hope you can get it sorted and enjoy the fortnight as much as I did!
Scarf