Does your pard's Single-Six 6-1/2" have fixed or adjustable sights? What style holster, in particular, is he looking for? Unfortunately, the host for my website, discontinued my images, but I could send him a Trailrider Products catalog...no charge. I have patterns and dummy guns for the fixed sight version, but it wouldn't be too much problem to make allowance for the adjustable sights.
If you would rather make your own pattern, take a paper grocery bag, wrap it around the gun....not too tight... and staple the seam edge. Cut out whatever skirt shape, flaps, etc. That should make a fair approximation of the leather if you use 8-9 oz leather.