I get essential oils from LorAnn... but you may be able to find some at JoAnn's (try the candy/baking section) or at a health food store. I'd probably try lavender... I love it, but it's too strong for the cat!
Actually, if you grow mint, you could also just chop up some leaves and scatter them around. I do that in my veggie bed to deter bunnies... Just be sure not to drop stem/root pieces, or you could find it trying to take over mini-ville!
