You can find them at stores and bakeries. Homemade is best, and bakery is best bought when fresh. :) I wouldn't recommended buying a carrot cake from a store that's been sitting there on a shelf for a few days.
Look up bakeries in your area. A bakery is sure to have a slice of carrot cake.
you can probably get it from somewhere like tesco, morrisons, asda.
At the grocery store or bakery