I'd do a websearch for yellow page ads for organic stores in each area you plan to visit. This is the hard part if you wish to wander at will everywhere!
Some major chain grocery stores now carry at least some organic produce and sections of organic dry goods. Larger organic food stores, in some areas, are few and far between. You may find an online source for organic dry goods that you could mail order in to a location you are staying at but the cost might be prohibitive.
If you choose to limit yourself to "only" organic--my opinion is you may have to find it where you can, yes maybe increase your storage capacity, but it may limit where you can travel and the amount of time you stay in more remote regions.
Good luck!