You didn't understand my comment, I see. Alright, let's go through this.
The rail on that pistol is NOT a scope mount. It's not a mount, period. It's there to aid in using the iron sight. Sort of like the rail on many shotguns, such as the Remington 870 Wingmaster.
Pistols are mounted with scopes. I would know this, I write for a gun website. For example, the Oregon optics company Leupold and Stevens makes the FX-II 2x20mm Handgun scope. However, the mounts are NOT on rails. They are usually drilled and tapped, which refers to how the scope mount is physically attached to the barrel. I think there may be some tip-off scopes, but generally they are normal type rings. I see no evidence, however, that that pistol is drilled and tapped. Therefore, you'd need to take it to a gun store (if it existed in real life) and have it drilled and tapped.