Actually, your question about extra cylinders is kind of a moot point as most shooters find it to be a PITA to knock the wedge, pull the barrel, and swap in an extra loaded cylinder and reassemble when you could just about load the empty one in as much time. I have extra cylinders for a couple of my Remingtons because it's a 5-second swap, but none for the Colts for the reason I mentioned.
Something to think about before spending 60 bucks+ a pop for a "spare cylinder"...