Mario Hanafuda are only available to members of Club Nintendo however decks can be obtained from websites like ebay.co.uk (where I got mine). A Club Nintendo member collects 'stars' and swaps these for goodies within the Stars Catalogue online. When this deck first came out in Japan it would cost a Club Nintendo member 400 points.
The actual deck follows the tradtional Hachihachibana pattern as used by Nintendo in their Daitoryo and Tengu decks and the deck itself is of the same quality as the Tengu deck.
The cards (like the Tengu and Daitoryo decks) measure 5.4cm by 3.3cm or 2.1/8" (2.125") by 1.5/16" (1.325") in old money. I have the 'European' deck so rules for Koi-Koi are provided in English, Spanish, French, German, Italian, Dutch and Portuguese. Rules for Hachi Hachi are not supplied.
Being a Mario themed deck, many of the traditional elements have been replaced by characters within the Mario universe. Here is the list:
Crane > Mario
Bush Warbler > Yoshi
Curtain with Luigi
Cuckoo > Lakitu
Blooper appears in the water by the Bridge
Butterflies > Paragoombas
Boar > Donkey Kong
Harvest Moon > Big Boo
Geese > ?
Piranha plant appears on the Sake Cup card
Deer > Wario
Rain-man and Frog > Princess Peach and Toad
Swallow > Koopa Paratroopa
Chinese Phoenix > Bowser