This is one I haven't seen before. If you have the box post a pic of the end label. If it came with a soft case only, there might be paperwork with the gun that has the Product Code and Spec. Ord. number on it. Post a pic of that paperwork.
Otherwise, when you open the cylinder and look at the frame under the barrel what is the Model Number (ex: M.65-5, MOD. 64-5, 65-4), and what is the Serial Number (three letters & four numbers)? Ignore any other numbers or letters on the yoke (the part the flops out and holds the cylinder). The s/n is also on the bottom of the grip frame.