Is there any link where I can download it?
That's a damn good question. You know, to be honest, it's been kicking around my system for so long I don't know how I come about having it. It maybe even came with a devkit?
I remember it was largely uneeded after early versions of powerup (as you say) where the loadseg was fixed, but I found it was a handy way of kickstarting the emulation.
What I found was that normally, if I try to run a pup program, even with the loadseg stuff in the emulation it failed with the "not executable" error.
So out of curiosity I tried to run the pup with runelf under the emulation and it worked.
Later I found that runelf itself was sufficient to get the emulation going, that is I do a "runelf >nil:" in my user startup. This silently fails because it doesn't run an elf file (none given) but it activates the emulated ppc.library and after that I found most ppc.library stuff just runs from shell as usual.
You could try searching aminet for it, I honestly can't remember when/where I got it from, but it has been a long time :-D
-edit-
You know, thinking about it, a simple thing would be to write a small 680x0 program that does OpenLibrary("ppc.library", 0) and then doesn't close it on exit. That would probably achieve the same result ;-)