Is it possible to buy Manga from Amazon Japan?
 

Or are there international restriction laws preventing Americans from purchasing and shipping certain items?

as long as they provide a shipping option i don't see why not?

i've ordered from Amazon UK and Amazon Canada before, but never Japan.

i'd try logging in with your account. if it allows you access to the site then there's a chance it may work?

^^^ Agreed.

I've purchased books from Amazon.ca a number of times. The shipping is expensive, but it should work.
(in theory)

There might be issues with regards to Region Locked media, but...I don't think manga is something that necessarily has that.

if you try and it DOES work let me know.
there's a few manga gems i'd like to maybe see about getting! :D

Books/CD/movies will ship from Japan no problem. I don't think they ship video games, and some other categories, though. So long as you're savvy enough to navigate to find what you want and complete the purchase, you're good to go.