Where's the application form for a Specific Purpose Visa??

Hi all. I cant find an application form anywhere - can anyone help?! I've tried ringing the embassy/consulate in London and they never answer the phone or ring back. I've also written to them and as yet received no reply. I really need to do this ASAP...I want to leave in 3 weeks!! And just to confirm, this would be the right application for a working visa? Many thanks. If anyone can help please do! Thanks!!!