Well we can check the first box of the Macdonald Triad...you wouldn't also be a bed wetter, by any chance would you?
I think I killed a fair number of them in the old Ulfheim, so maybe try Ruins of Utheim? Might be faster killing to check some of the lower tier forest-y scenes. I don't know that I've ever really see a lot of them at once anywhere, though, but I think you see them more in wooded areas.
The RISE OF THE SQUIRREL SLAYERS!! I think we need to form a guild. We sit around the campfire and tell stories of our epic battles with the squirrels.
I believe there is an NPC in Central Brittany that will try and sell you a squirrel. Don't listen to her though, she is stark raving mad.
The best way to kill squirrels and cute little bunnies is by having your wild board pet attack it. Trust me, it's hilarious.