Doll Island in Mexico. It's one of the most spooky-looking places that gives chills and thrills. There's something about dolls that inherently fascinates and bothers us. Use that to your advantage -
You can ask friends and family for old dolls, but you can also find bags of them often times in thrift stores like Goodwill.
If you start now leaving them outside, they will age naturally in the weather but you can accelerate the process with bleach, sandpaper, and dipping in water with paint drops in it. Be creative with the process: Tear clothes, rub away makeup with sandpaper, put fake spiders in the clothing...
When I left my Shirley doll out in my circular garden, I referred to as "doll island" the ants took over after a monsoon rain.