I cannot vouch for their authenticity, but Hartford Chiefs caps are available for $10 each at the merchandise store of the New Britain Rock Cats, at New Britain Stadium. I could not find them in the Rock Cats' online shop, so you'll just have to go to a game -- which will be fun, trust me. The hats are one-size-fits-all.
By the way, why doesn't the City of Hartford sell merchandise like this online? Doesn't it have a slight revenue problem?
The Chiefs were the Boston Braves affiliate in the Eastern League from 1947 to 1952, playing in Bulkeley Stadium. Before that, they were the Hartford Bees. Come to think of it, maybe this is a Bees cap. If anyone knows for sure, drop me a line.