We have drugs around everywhere: inside houses, carried by zombies, dead bodies resulted of a probable mexican standoff… also, many houses have underground storages of guns, weapons, medicine…
…in other words, people used drugs and were paranoid. That means that whoever was the supplier had to be EVEN more paranoid, and also cautious to avoid government action against them.
So, somewhere in New England, there should be a industrial facility to make and distribute drugs. Good place to find raw materials for various crafts, not only illegal drugs, but medicines, mutagen, and so on. Also good place to find REALLY high survivors, and weird zombies.