Search vendors of dehydrated/emergency foods, and some will sell brand-new MRE-equivalents. USGI MREs are not legal to sell unless surplussed, and by then are of somewhat questionable value. However, the civvy equivalents are brand-new, and of greater variety. Another search term would be "retort packaged foods", "retort" being the key term.
Like most food items, the temperature in which they item has been stored is critical to its shelf life, and nutritional value. The lower the temp, the better, generally speaking. Most vendors surplussing MREs have no idea under what conditions the item was stored, and so sell them off at a considerable discount. Truth be told, and IMHO, I wouldn't consider surplussed MREs OK for eating unless the production date was less than 5 years from current date. Some iron-gutted types might disagree.
Just my opinion, most surplussed military MREs are over-priced, giving their inderterminate storage conditions. In this case, the buyer is really buying a pig in a poke.