I too have yet to find one on PC/NA. Since the hotfix, I've seen them only on PC/EU.
I think that this might be a problem with how instances work in ESO. In order for an instance to shut down, every single player must leave it, and the instance must remain empty for 5 minutes.
The EU server experiences extreme population swings, in part because it doesn't have a lot of people from other regions playing on it, and this is exacerbated by how pretty much all of continental Europe is squeezed into a single oversized time zone. So compared to NA, EU experiences much higher peak populations during prime time, and much lower populations during off-hours.
The (relative) lack of deep valleys and high peaks for NA population counts means that there's probably far less instance churn on NA than there is on EU. Old instances aren't really emptying out completely on NA so they aren't getting shut down, and the peak demand period isn't as intense to generate new server instance spawns.
I could be wrong and only ZOS would be able to say for sure, but based on what I've seen in the past and ZOS's own comments about EU-vs-NA population patterns, I believe this to be a plausible explanation for why these new instances aren't appearing on NA.
I apparently found one on day 1 since that's when I got the achievement. But I don't remember seeing one since. Not until yesterday when they were everywhere.