+ 1 for Ruger customer service. I have owned many, many Rugers. The only time I had to send one back for service was for a Vaquero in .45 LC. It was shooting way left, off paper. They turned the barrel, replaced the hammer, replaced spring in ejector rod, and cleaned, sent back...no charge.
My Single Six came used with both cylinders. I would defintiely go to Ruger for a matching/fitting piece. By the way, from the several Single Sixes that I have owned, the LR shoots better. The Mag is great to have. Just my 2c