Umarex USA makes the H&K pistol. I suggest you contact them. See the link below
I beleive AirsoftMegastore recently got them in stock.
See the link below
Open the link below and read the section on (REPAIR/SERVICE)
If you are asking about the Crosman C02 pellet pistol then Yes that is what it is designed to power the pistol.
No.
12g,
It won't fit in the pistol.
Get the pistol, preferably a 1911, you get better velocity, and a smaller easier to carry pistol.
The c11 co2 pistol shoots at 480 Feet Per Second (FPS)
no it will ruin your gun if you do
It is possible.
It was designed for BB's .175 or .177