A cylinder can be bought in any number of places. Ebay being just one of them. To get one cut for moon clips, is going to take a custom shop. TK Customs comes to mind but there are others. They can also fit the cylinder to your gun (which will need to be done.)
There is one for sale over at arfcom on page 5 of the handgun parts for sale. Derek45 has it for sale and it has been listed for awhile, I believe he's asking $80 for it. hth