A few weeks ago, canned coffee maker, Dydo, began to release these little Super Mario figurines with some of their canned coffees.
One of the clerks at a local Family Mart started displaying these near her register one day. Recently I asked about them, and she pointed me directly to the coffee.
They seem to be only available on DyDo Blend, both regular and "Demitasse Coffee" versions.
These coffees are available both cold and hot, so if you're looking for them, check both the refrigerator and the shelves near the register.
And overall, there are 8 different character available. It seems that Mario is pretty common, and easy to find. I don't know if they've intentionally made any characters rare, but the sticker on the case shows which character is inside, so they aren't randomized, or anything.
By the way, if you're interested, some of the character names in Super Mario are different in Japan. Mario, Luigi, and Peach are the same: マリオ, ルイージ, ピーチ.
But, Bowser has always been simply referred to as Koopa クッパ. Goombas are Kuribo クリボー. Koopa Troopas are Nokonoko ノコノコ, which is an uncommon Japanese word for unconcerned, or nonchalant. Lakitu, which sounds Japanese, is Jugemu ジュゲム. And Toad is Kinopio キノピオ. Kinoko キノコ is Japanese for mushroom, so that fits. :)