Really there's not any pure one's anymore, not from the ones way back when, and if any were to have surived,You wouldnt want them, Because they would be inbreed big time, they would be small as banty's get sick easy, if they did lay at all it woulnt be much and the hatch ratio would be somthing like one in a hundred. you have to put new linage in .In order to keep stock healthy and productive. and since chickens purity is based on color size and conf. its not that hard. Take Boar goats for instance only a few could be had, so they were inbreed back with each other and you couldnt keep them right side up after a while, and since other goats coudnt be matched with them ,they started Reg. them as 100%,pure, 75%pure, 50%pure and so on. you breed a 100% with a 75% and have a 85% then beed 100% with 85% and have 95% and so on until your back at 100%. This is done on all livestock.