Not that I know much about actually recording IEM's, you won't find too many folks that will help you right off the bat.
Number one, if they are going to help, they probably DON'T want you spreading high and low and risking their chances/abilities moving forward.
Number two, most decent IEM recordings involve recording more than one feed.
Your best bet is trying to contact someone that has recorded GnR IEM's in the past AND shared them, and see if they will help you.
You're far better off, getting a basic AUD MIC setup and recording that way.
I have had the chance to learn how to do it, and the only reason I would ever tape an IEM is to get soundchecks. I wouldn't bother with doing an actual show, unless I was outside the building.