I think at the very least the humane society should be responsible for "the deed" of culling your entire flock for you, free of cost. Be sure to let them know that you loved these birds and that they were good layers, and that you hold them solely responsible. They may get a rude awakening and a valuable education in poultry rescue if the problem came back full circle and landed in their lap and they had to face the consequences of their actions. Doesn't matter if they are a "rescue" or if their heart was in the "right place" your entire operation was compromised and is past recovery. Shame on them and they ought to pay you for your loss.