The last time Ayu was in LA, I asked someone to get her autograph for me, and she did.
I was unable to make it to LA myself and she was nice enough to help me out. I don't know anything about the autograph through Avex or whatever as I have never tried that. I would suggest the next time she takes a trip to the US, which I'm hoping will be soon, keep up with the fans here on AHS, as a lot of them go to meet her. Maybe you can ask someone to help you get an autograph like I did.