I ended up buying this Expedition Case by Power A for fifteen bucks. It’s not perfect, but it’ll do. It includes cartridge pockets (6) and stylus holders (2). My only complaint involves the 3DS compartment’s loose fit–about a quarter inch of space lengthwise and width-wise for jostling around. I stuffed it with foam packing wrap from the original 3DS box. It’s not the perfect solution, but it does offer a bit of protection while still fitting a large jacket pocket.
My semi-retired fat blue DS isn’t happy about its “spoiled brat” successor, and I’m not surprised (When it first saw the newcomer’s 3D screen, it shouted “Witchcraft!” and hurled a stylus as a “howdy” gift).
If any of you have bought a 3DS case, please chime in with a description and the pros/cons of your purchase!