Park Slope's Fifth Avenue has yet another gluten-free friendly spot: Fleisher's Grass-Fed and Organic Meats. A friend tipped me off to the fact that this gorgeous old school butcher shop sells some homemade gluten-free products, among them various sausages, meatballs, and savory pies. (Thus far, I've sampled the meatballs and they were delicious.) They're also a full service butcher shop, so you can buy gorgeous cuts of meat, which are naturally GF.
Lest ye worry about their GF practices: These folks GET IT. While not GF themselves, one of the owners had a celiac in her life and knows best GF practices. To that end: The meat products are made in a dedicated GF area and a list of ingredients is attached to the meat case for quick and easy reference for staff. The savory pies ARE made in a mixed use area - a fact which was made clear to me by staff upon my first visit, thus allowing me to make an informed decision based on my particular comfort level/level of gluten-sensitivity.
One last note: Fleisher's is fantastic and the neighborhood knows it - so they are BUSY. If you have your heart set on a particular product, may want to call ahead to make sure it's available.