Note that the Verbatim BD-50s sold in Japan are no longer actually made in Japan, they're made in China, and a lot of people have been reporting write errors on them (the top rated reviews are all 1 or 2 stars and mention errors): http://www.amazon.co.jp/product-reviews/B0043SEMMW/ref=cm_cr_dp_see_all_summary?ie=UTF8&showViewpoints=1&sortBy=byRankDescending
I personally use That's (Taiyo Yuden) BD-50s: http://www.amazon.co.jp/dp/B00GJ95LB4/ , which are made in Japan. Used to use Panasonic ones, but nowadays they're only available in Japan from resellers and not directly from Amazon.
That's BD-25s and BD-REs are pretty good as well, but their cheaper BD-25s are made in Taiwan now.
Amazon JP won't ship these outside Japan, but you can go through a forwarding site like tenso.com or check and see if anyone on eBay has them.