try this
http://www.ebay.co.uk/itm/20mm-20mm-raising-weaver-rail-fit-rifle-scope-adapter-mount-Base-/181104725468?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D6563632624314125982%26pid%3D100011%26prg%3D1005%26rk%3D3%26sd%3D261160986151%26