Dear Giovanni,
Good luck with your research. I too went on to London (and Bristol) to do research on Kane. Be sure to visit the V&A Theatre and Performance Archive as they keep the Royal Court Theatre materials there and have some interesting things on Kane.

i found it ones by searching google for something like ' sarah kane interview'  maybe + audio or something... (it was a mp3)

Upon looking at the citation in 'Love me or kill me' it does not appear as though the interview was published at the time of Saunders's publication. I work at a library, so I can do a bit more research for you on this, but as it appears right now, the interview you mention may be one that Saunders did privately with Kane for the purpose of scholarly research. I'll keep you posted on what I find. If I cannot track it down, you may be able to contact Graham Saunders yourself and see if you can access the interview somehow. He is a rather pleasant person and I am sure he would be enthusiastic about your interest in Kane's plays.
All the best!