The primary bump stops are inside the coil springs. I'm not aware of anyone making longer ones. The outer bump stops are nowhere near bottoming out the springs. They only limit upward travel during articulation. As others have said, unless you have a clearance issue with tires or something, there's not much reason to move them. You can't hit both at the same time unless you're doing something extremely crazy and likely you'll only do it once...
I have a different issue in that my springs have no bump stops internally and I cannot add them (air bags), so I may drop my outer bump stops because I do bottom out sometimes, and when it does, it's a very hard impact with no bump stops. So I have looked at relocating these for a different purpose of acting as the primary bump stops. The problem is that they are very firm and small, so they will be both harsh and possibly too thin and you may be able to blow right through them if you hit hard enough. Hopefully that never happens!
Also - you can just take an aluminum block and drill two holes in it or take a piece of 2" square tube cut to length and drill 2 holes in it as well. These are so easy to make for less than $10, I'm kinda surprised anyone is selling them. You can also buy a piece of 2" aluminum flat bar in say a 1/2" thickness for about $25 or so and cut a bunch of plates and then stack them for the exact amount of adjustment you want.