Look at it this way... anything that exists in sufficient numbers for giant commercial hatcheries like Ideal and Murray McMurray to list them in their catalogs, AIN'T endangered in any conventional meaning of the term.
However they often aren't really suitable representatives of their alleged breed, either. (That you can order a whole bunch and find *some* that suit the standard, at least kinda, is entirely different from having been bred for a number of generations with hard culling to produce a line that breeds true and are nearly *all* in accordance with what the breed is supposed to be like)
Certainly there is no reason a person shouldn't order up a few Delawares, or any other quote endangered breed unquote, with their next big hatchery order... but it's just for purty, just for fun, it is NOT helping conserve genetic diversity or bloodlines or breeds.
If a person genuinely wants to help CONSERVE A BREED, you need to make sure you're starting with good representatives *of* that breed, from longstanding good lines, and then you have to be in a position to produce a considerable number of chicks and cull down (one way or another) to the ones you want to keep for breeding pens.
-and that's breeding penS, plural, not just one trio or something like that. Animals (and some plants) are not just something you can xerox onward from one generation to the next -- if you are not
actively selecting for traits (meaning, producing enough individuals to choose only the best to breed from), the gene pool "wanders", and sometimes it doesn't take many generations to stray considerably from what the population once was.
There is, of course, nothing whatsoever wrong with just having a few birds for your own enjoyment, which is different but perfectly fine
Good luck, have fun,
Pat