LOL - how many sizeable operations marketing Gurnsey cow A2 milk can you name? Don't think that ATM's market stake is threatened by a boutique producer (their words, not mine).
But sure - and don't forget our very own diary herd in Canterbury; Current headcount: 1 (Dexter / Jersey cross). We are producing only A2 milk as well ;); I am sure ATM is shivering in their boots ;);
Percy - I think roughly 20 to 30% of all cows are producing A2-milk. The trick is just to identify them (its not just breed based - there are as well Jersey cows producing A1 ... though it is a smaller number), separate them and make sure they are bread separately and their milk is processed separately without contamination. Not cheap (until you have 100% pure A2 herds) - but absolutely, it can be done.
BTW - There is a reason that there are not that many Jersey herds around ... They do cost more in maintenance - Jerseys produce marvelous and creamy milk, but they are quite bad in looking after their calves (meaning higher mortality or more human intervention required). But hey, nothing you can't fix with throwing more money at it.