If you buy a whole goat or sheep you can cut it up any way that you want - or have someone do it for you. The reason why a butcher may be reluctant to give you this special cut or that special cut is because it will leave them with a whole heap of unsaleable meat because nobody else wants the leftovers from the special cut at a price that makes the special operation worthwhile. And yes, I have bought a whole sheep before. But that was back in England from the farm gate. I've never tried to do it in Argentinaor lamb?