There are a number of taxi companies in the area I have only listed one from each area below - please check with them that they can deal with large numbers.
If they are unable to help they may be able to recommend another company.
AVIEMORE:
Aviemore Taxis - 01479 811 111
Bremners - 01479 810 141 (minibus available)
GRANTOWN:
Strachan's Private Hire - 01479 870025
Woodlands - 01479 872 289 (minibus available)
INVERNESS & AIRPORT:
Central Taxis - 01463 222 222
Text-a-taxi: 07867 977233