The covetous 3DS Case is now back in stock on Club Nintendo! I've been checking the damn thing's page nearly every other day for a few months now, and it looks like Nintendo is now finally able to meet the demand. You can head over to Club Nintendo's website now and get it for 250 coins.
If you're confused on how to choose a certain 3DS case, don't worry: the set comes with different inserts, including various Mario, Zelda, and general Nintendo artwork. Considering the 3DS' library is fairly robust at this point, I won't have a problem filling it up: especially come this Summer, when a whole bunch of marquee 3DS games are set to be unleashed.
3DS Game Card Case [Club Nintendo]