Oddly enough, I bet someone at Avex would have to speak English.

That's not saying that why should try that or anything. XD But I definitely think it might be a good idea to call up Avex and tell them what we're doing and see if they'll even accept this first (I don't think they'd say we couldn't do it, but maybe that they don't allow those sort of things to be dropped off for their clients... :/).
And I definitely agree with whoever it was that said that it would be more convenient to send the letters to someone closer to them geographically. So it might be better then to write down on the first post where the people live so we can send it to them accordingly (I think you already mentioned this XD).
Unfortunately, my Japanese is only proficient and the people I know who are Japanese and from Japan are all studying in the States (and are currently back home in Japan so I couldn't call them), so they wouldn't be able to hell us either.

Someone's gotta have some hook-ups in here someplace. :/ I know at least one person on AHS who's fluent, but there's gotta be more....