Endless supply of wolves can be found in Nen Hilith, just west of Celondim. Other than the southern area of Erud Luin, wolves are sort of scarce. There are a few around gondamon.
The good news is you can kill wolves that are grey to you and they still count. So even if you skipped this accomplishment and are now very high leve, you can come back and pick up this deed whenever you have time to slaughter 60 wolves.