At least for some guns that isn't true, OldStony. You can get ready fit recoil pads for some models of the most popular shotguns like the Remington 870. The pardner pump is near clone of the 870, which is why I suggested that an 870 pad will work. Most local gun stores even carry them as does Bass Pro.
You are talking about a grind to fit pad, which is what is on my Browning, but some of the pad makers may even make a dedicated pad for an 870. Check online for Limb-Saver, Kwik-Eeze, and Pachmeyer.