Outer Limits 4x4 Board

I have a bottom end in the she that is in pretty good nick. I was removing the lifters today and noticed one was a little pitted where is follows the cam. Can i just replace one lifter or all of them? Do i need to replace the cam as well?

Any idea where i can get these parts from? If i get another cam i might as well put something different in that is more suited to my needs. Is Joel from PGS still on here??

Jimmy