Hi sikpuppi.
I am aware that Aer Arann also do charters, especially out of ORK, but I dont think their ATR's might not be big enough for 70+, if that is going to be your number. There should be no problem if you require them for a weekend shuttle, as they do have a spare a/c at Cork during the weekend, as far as I am aware.
Ryanair have been know to do charters as well, if it is a weekend as well, they would have spare a/c in Dublin, so it might not be too bad. As far as I am aware, the have 737-200's with seating for 130 odd up there, so it may be more to your liking.....