I recently got one by posting in the Buy, Sell, Trade room. You might try that.
I got the hooked and for me it's perfect. It allows me to get my pinky on the grip, which I can't do without the extension. Glove size isn't going to be accurate as I'm sure that is a combo of finger length and width. Better to buy one and trade/sell it if it does not work for you. Otherwise, you will just be guessing.