I did some research a bit ago for a client considering purchasing a Mills Act property. I don't remember too much specifically but I do remember I had to be a bit specific about the search terms since I was only interested in Orange County then as you are.
Take a look at this link for information for the city of Orange and their application process.
Brian Wilson, Realtor
You can call the city to find out if they have a list of the homes, I believe each city would know what homes they have that qualify for the mills act