It might be in your best interest to get tested... You can either cull them (sad!) or if you want to give them away, just do so with full disclosure. "My flock might have Marek's disease, which is a highly contagious virus to other chickens, and it is often terminal once symptoms show. You are adopting these birds at your own risk and by taking them you agree that you understand what Marek's disease is and how it is spread.". I doubt you'll get many takers, but it is about your only option. It is VERY IMPORTANT TO NOTE that depending on the serotype of Marek's you have (or don't have...) any other flock might be carrying a different type. This is sort of hard to explain but essentially the different strains of Marek's will show the SAME symptoms, but a chicken that is immune to serotype 1 Marek's may not be immune to serotype 2. Essentially, unless you know exactly what your flock is infected with, even giving them to someone that already has Marek's in their flock can be risky. They might be carrying a different strain. You could do harm to BOTH flocks in this way.