I've gotten some great birds from Darling Poultry (West Gardiner) and from Feel-N-Froggy Farms (Plymouth). There's a lady in Lubec, Noelle Barbaro, who sometimes has really nice Chocolate Orpingtons available, but I don't think she's very active as a breeder these days.
The Maine Chicken Enthusiasts Facebook group is a great place to start your search if you use FB.
If you aren't picky about breeds, people seem to always have backyard mixes available. I usually sell mine for $5-10 depending on how old they are.