no subject

That depends. There are pokemon you can come across enough but not many trainers have them. Shellos is that way, I think. Things like Shuckle can be found if you look enough in the right places, but I don't know if people just haven't looked or if they decided they didn't want them. Then you've got the pokemon you could never come across in the wild, but thanks to breeders it's pretty easy to get an egg, like Eevee or the fossil pokemon. Or you can have any pokemon and it will be considered rarer if it has a different coloration than usual.

Pokemon that I can say for sure are rare on all accounts are the legendaries. They only show up for certain conditions and as far as I know have never been caught.