I don't know if marek's is common in my area or not, but I still had my chick's vaccinated at the hatchery. If I were you, I wouldn't give up on chicken's all together, maybe try having the next batch vaccinated and see if you are more successful in the future. They have to be vaccinated newly hatched. But since there is no cure, I thought I better not take a chance.
Good luck, I'm very sorry for you losses.
Good luck, I'm very sorry for you losses.