RailKingJP has his own website, and it seems that on a weekly basis he features some item available at Shosen Grande, the bookstore at Jimbocho which has floor for railway books and goods.
Anyway, this week's special is a pair of mugs that I haven't seen before (not the Kenelphant ones). The YT video is private, I don't get if you're not really supposed to repost it or not, so here's RailKing's page with the embeded video, from which you can click through to YT if you want to: http://railking.jp/goods/character-goods/2017/01/21/20170121/ . These look cool.