Still doesn't make sense. The cartridge is the replaceable part of the valve. Why would you want to put an old cartridge in a new valve. Why don't you just replace the old cartridge with a new cartridge for the same valve.
I believe the OP is referring to keeping his old brass valve in the wall, but replacing the cartridge, handle and faceplate with new and modern hardware. I myself have never seen such an item, but can see the usefullness in it.