Can't find frozen cranberries anywhere. Can I use fresh instead in my cake recipe?
Frozen cranberries usually do not have added sugar, and are usually frozen whole. So the sneaky solution would be to buy fresh cranberries, freeze them, and then use them however the recipe calls for :)

Since you're not worried about long-term storage, a few hours in the freezer on a baking tray should get them to the correct consistency.