Order directly from Ruger.
The neat thing about Ruger rings is that you typically only need to order 1 ring to change height. They come in 4 heights. Low, medium, high, and extra high. They come from the factory with 1 medium ring which goes on the front. Place the high ring on ring on the rear for scopes up to 40mm. If you want a higher setup just move the high ring to the front and order an extra high for the rear.