To sum it up I expect to be 2KYUU level by the end of the year . I could work more to get 1KYUU next year but I have something else on my mind : thanks to my school  I'm going to enroll in a japanese university (waseda or tohoku according to my level) and then start an internship in a japanese company for 6 months . So it seems to me that the next step ,as something unavoidable for anyone willing to work in a japaneses company,  is to really improve my keigo.
So do anyone know about a reference for this complex but sensitive problem ? japanese themselves have a hard time with it so I guess a specific training for several months could be useful to be able to be operative in my work.

Read about this book 新版人に聞いてもわからない日本語知識辞典 but the scope seems a lot larger than mere keigo ....it's more like a book to litterate native-like fluency .
And I'm more looking for a book dealing exclusively with keigo .