All the plastic butt plated 525's are individual, some swap over by coincidence but not all. I have 2 525's and they are slightly different to each other. I have but the 15mm Isis pads on both mine as well.
Very annoying that there is not. I remember needing one on mine years ago. Beretta make a range of pads for their guns. But as has been said, ISIS pads are the best anyway. It just means you have to get it fitted to the gun.