While I could not find a replacement button for my Wacom Intuos 3 tablet's stylus, I did find a 3D printable replacement. However, it did not stay in the pen, it would not attach. So I modified it to have a buckle where the previous one had a pointed rectangular extrusion. Works perfectly for me. Don't be afraid to use a tiny bit of force when pushing the buckle into the connecting hole! I even designed it to be (hopefully) possible to remove, but you'd probably need a pair of pliers.