Hmmmmm. How 'bout y'all remove your stock bumps now and drill right thru the whole thing and add a 4" X 3/16" bolt? That way you'll never lose the rubber pieces ya have now. It's just a thought. I wonder what's holding those things in place? I checked the VX electronic parts catalog and I can't find part numbers or any mention of any type of bump stop at all. Nothing wrong with being pro-active on a potential problem, although it's not a big problem. If ya wanna use new mounting bolts, they're M10 x 1.25 x 25.
Mark