I had that same problem myself recently. I ended up just going to Gusgen (was level 18 at the time) and joined the alliance doing GoV there. Everyone was super cool and we pulled ghouls every once in awhile to keep trying for the skull. Eventually someone switched over to a high level thf and cleared the place out. Couple hours later I left with a skull at level 24. Just make your way there, it'll be worth your time in more ways than one.