My experience has been that the 7 Mag is about the second or third most common 1S, if you count the 45-70, which I don't, really, with it's 22" barrel.
I have seen quite a few on the auction sites on a fairly regualr basis, but they are usually later production and often with the black pad (good if you value the Ruger barrels). I have not, however, seen many in gunshops or at gunshows over the years. Not sure why. The 1S is one of the harder variations to find on a regular basis, either due to production numbers or the fact that their owners tend to hold onto them (like me).
Cutting any No. 1 stock ruins the rifle for me, and unfortuantely, very few seem to be executed well. When I shoot any of my magnums, it's usually with reduced loads anyway, so the OEM recoil pad is not an issue
LC