get a sheet of the color you want nylon, just cut and shape yourself? it would simply screw in between stock and pad? you already have the 2 required dimension to sand it down too. the reach you can take from your arm to determine the sheet nylon thickness needed. Maybe the part change would be screws that hold pad in would be longer, easily obtained at say Lowes or a Tacoma screw in stainless*… sounds like a fine off season fun project... way cheaper and probably much quicker turn around than going thru a smith in the off season!
i have done this to an older version of a marlin 45/70 that felt like a kids bb gun in my hands... i added to the reach with a piece of black nylon and added a very thick pachmayr recoil pad. really made a difference in fit and how it shot for me...