Plume fossil early

[RebornFan7]

So I've heard you can get a plume/cover fossil early if you defeat a pair of meteor grunts that you find in the museum. I found the grunts, and they told me to go meet them in Tanzan mountain, but I can't find them. I have beaten Noel. Do I need to fight more gym leaders for the grunts to appear at Tanzan mountain, or is there something I'm missing?

[Rendolf]

I think I remember that quest not working for me either, and I never did figure it out. Apparently you can't do it after clearing the Tanzan Base, but other than that I'm not sure.