My experience has been that campground hosts, rangers, and the folks in the office can all tell you where to buy wood nearby. Moving wood from one campground to another is highly discouraged if not outright illegal due to various non-native insect species such as emerald ash borers, woliaed aphids, gypsy moths, etc. Wherever you go, do NOT stock up. Buy only what you plan to burn where you are, and leave any leftovers for the next camper. Yes, it’s more expensive, but the locals appreciate your not infecting their woods with new pests.