Adding to my last post: The spout I'm using is grey, standard Sigg style cap. It has a small (quarter inch outside diameter) clear tube, just about an inch long coming out of the base of the handle at about a forty five degree angle, and has a tiny vent hole near the base of the handle (on the outside) on the other side. A finger on that vent hole keeps fuel from flowing until you remove the finger. It has "SIGG Switzerland" across the top of the handle. I did a quick check of the Sigg website, and all I found were water bottles. Maybe dig a little deeper or contact them.
I have used another version where the tube and the vent hole were in the saddle of the handle. I think I remember that these were a cottage industry product, but no idea who made them.