I'm not sure about where to find them, outside of chicompany or one of Coca Cola's suppliers, but I was able to track down the official part number and dimensions for the o-rings on pin-lock posts:
Black: Hansen P/N 902-A-292 (Coke P/N 15312) - 0.450 ID x 0.658 OD EDPM
Red: Hansen P/N...