So ok, I understand your intentions are good and you’re not like trying to trick them or anything but actually doing something to help their cause, which is pretty amazing (congrats on your other fundraiser too, impressive!) but it is kind of impossible and I’ll explain why:
A) You’re in the UK, if it were to happen, it’d have to be sometime around their tour schedule in the UK (and only if they were playing in or near your city)
B) Being outside of their homecountry means that moving gear, crew (I mean everyone, techs, chefs, production, management, security) and everything else is 10 times harder. Yes, they do keep a rig in Europe, but imagine how crazy the cost would be
C) Actual cost. You might raise lots of money for MFR but they will need way more than that to come and play simply because of the reasons in b. Also, I imagine that you’d have to book a small venue for the gig and that requires more money from your school to provide for booking it and since LP is a pretty big name, it wouldn’t be cheap.
Bottom line is that it would cost way too much for your school to organise this than have a local lesser known band (or a band from your school if you have one) play and that its way too much trouble for LP’s team.
You can always do the fundraiser though and donate the money to MFR, I’m sure they’d appreciate it a lot.