Have you considered calling the airlines directly for group fares? I helped a church choir book get info on summer flights to Rome on
Delta and the fare was alomost 35% cheaper than the posted rate. (I'm not a travel agent, just a
supportive parishioner).
It just takes a few phone calls to various airlines group desks. At that time they gave 1 complimentary ticket for every 15 booked.Their trip was last summer.
Blessings on your work and travels.