I don't think anyone makes afrermarket caliber conversion slides or barrels for the SR series unless Ruger will sell you the 40 S&W slide, barrel and recoil spring assembly from an SR40C
The SR40c slide is .060 wider than the SR9c slide, that is where it gets the extra mass to handle the .40 S&W round, however they use the same recoil spring assembly. It would be better to just buy a 40c than to try a conversion and probably not much more expensive, everyone should have at least one of each anyway.
