I suggest you to hunt them on Edron Mountains during Rapid Respawn or when they are boosted, I did the task there and with Rapid Respawn it was a good spot. But eventually, there is a Wyvern "raid" that happens inside of Mushroom Gardens in Gnomebase Alpha that comes up with the message:
"There is a sudden rise in wyvern population in the mushroom gardens beneath Gnomebase Alpha."
They share the respawn with Crystalcrushers, but you can hunt them there as well. If I'm not wrong, when that raid happens, it's like a permanent increased density on respawn for them, just like other raids for example Edron Orc Berserkers and Ankrahmun Ancient Scarabs. When I was at around level 80 I hunted there and it kept spawning lots of Ancient Scarabs, it only stopped after Server Save, so I guess that Wyvern raid is the same mechanic as those other raids. It's not a regular raid where you kill all monsters and the raid ends, but it stays "active" until Server Save (atleast when I hunted there, that's how it worked). You can try it and tell if it's good or not.
Good luck!