Now available at Nintendo NY (Formerly known as Nintendo World Store).
Cephalopod Cousins are 19.99 + tax each.
Squid Cushions are also $19.99 + tax.
Judd and Green Squid are 9.99 + tax I believe.
According to NintendoNYC's twitter account they came on Aug 25. I took this pic on Sept 5. They are keeping them well stocked apparently.
The difference between these and plushies imported from Japan is the tags. The ones in Nintendo NY are bigger and besides for Splatoon in Japanese under the Splatoon logo, everything else in the tag is translated as well as saying it is distributed by Little Buddy and information about that. The English names are used.
If you can't access the Nintendo NY store easily the price is not much different from buying off Amazon. You probably will most likley get one with a Japanese tag though if that affects your buying decision.
Edit: I actually see an obvious difference now. The earrings are different. Japanese plushies have shiny, smooth fabric material while American ones have felt as earrings instead. For comparison I put Japanese Marie plush on American Marie plush and American Callie plush on Japanese Callie plush to show the difference better.
Also it is hard to really tell if one is a bit bigger than the other or because I really handled my older Japanese plushies a lot that they sort of had their stuffing/fabric shift over time changing their shape a bit. It could be luck of the factory draw where sometimes you could have a slightly larger one but someone else could have a slightly different looking plush either from the same run or due to it coming from a different run. The ears look a bit different especially comparing my Callie plushies. The earrings are definitely the main difference though.