Gun Walker is an original model created by SF Paper craft from Japan.
In games there’s a lot of model similar to Gun Walker here for example in Metal Gear Solid V , a similar model called D-Walker where Dr. Emmerich build for The Skull during his confinement.
Later it was used by Snake in his mission.
Tho I never used it even once to go on mission, I found it restrictive compare to doing normal sneaking.
In some maps you would be able to capture D-Walker and sell it to upgrade your base.
Models requires 3 piece of paper, comes with picture instruction guide and easy to build.