Ruger makes extension rings but another option is to just choose a long scope with lots of eye relief. For example, a 3-9x40 Zeiss Conquest will fit perfectly in Leupold 'lows' without the need for extension rings.
+1......What PB said.Here is one (Leupold 4-12) with Ruger extension rings. 7MM STWHere are 2 with Ruger low rings. Top is 3-9 Zeiss, bottom is Zeiss 4X. Both 257 Roberts