As others have mentioned Gamo has discontinued these. The only one piece they sell is not adjustable.
RWS has a nice adjustable one piece mount that I have used and like for certain situations (350 mag comes to mind)They are very sturdy and very well made....They are expensive though.
RWS has some less expensive 2 piece adjustable mounts that are pretty good as well for guns with less recoil.
BB Guns, Pellet Guns & Air Rifles at