Recently BK1.jp became Honto.jp. If you migrated from BK1 to Honto, as a foreign customer, you should still be served as before. But if you’re a new customer, there is a certain clause that requires you to have a Japanese Mail Address.
Here is a post a blogger made to help you guys register with Honto: http://kaizora.wordpress.com/2012/05/19/how-to-signup-for-honto/
And here’s a guide a kind Anonymous made for new folks who wanna join and buy from Honto.jp