I am certainly no expert, and I do know there are those here that come close to qualifying as experts. I'm sure they'll chime in, but that's not an ameraucana. Pretty sure, and as mentioned the experts will correct this if I'm wrong, but pretty certain the purebred 'ameraucana' will have a beard from the time they hatch (what you're calling the collar of feathers). When I bought my 8 back in Feb, first thing I looked for was the beard, if they didnt' have the beard, I knew that breeder wouldn't be selling any to me. Now, not that I wouldn't have been satisfied with some EE, but don't try to sell me an EE calling it a purebred, at purebred pricing.....
as far as 'not common' to get ameraucanas, well there are a LOT of breeders, but you're right, not a breed usually sold at the feed stores or big hatcheries.