NOTE: EBBETS CAN NO LONGER TO SINGLE PIECE CAPS AT THIS TIME
Since I've been writing heavily about Ebbets Field Flannels lately, I figured that I should mention that EFF recently brought back the option to order a single custom-made cap, for the price of $99. If there's an obscure retro team that you are dying to have a cap of and you're willing to pay the price, this is your chance. There are several styles and variations to chose from. Just go to Ebbets.com/category/Custom_Caps and scroll to the bottom for more details.
I had a 1962 San Jose Bees cap made, and it turned out exactly the way I wanted. I was extremely happy and I plan on having more custom caps made in the future. Take note that unless it's a cap Ebbets has made before or they already have research done on the logo, you may have to provide them with pictures and logo artwork of the cap that you want made.