Holy CRAP! I was visiting the desert area on Crystal Isles, there's this small valley filled with nests and *dozens* of griffins. I kid you not, this is the place to be. A lvl 150 just randomly started chasing me when I was scouting levels. Long story short, best friends now.
If you have access to a snow owl, you can tame these with any crossbow! Just shoot it until it looks bloody, and heal it with the snow owl’s ability. Do it so that it heals quite a bit, but not so long that the torpor drains back empty. Then hop off the owl and continue shooting it with tranq arrows. I knocked a 140 with a 279 crossbow and using this method it had over half hp remaining once it finally went down.