With level 60 every player receives a letter to learn flying and to buy a flying mount in Honor Hold for 300 gold.

Also Druids.

But Druids don’t need to learn flying und to buy a mount; they can learn the Flightform spell for 3 gold who includes the ability to fly. Many Druids waste 300 gold or think they can't afford flying and ride sadly through Hellfire.

My suggestion is to send an adapted letter to Druids, suggesting them to learn Flightform.