I am not sure. I checked Amazon and their selection is barely existent and not particularly reasonable in price. Have you tried Fancy Feast Classics? They have a very similar ingredients list, are readily available, and very reasonably priced.
Have you checked locally? Purina has wide distribution.
Well, I may be wrong about Purina One. I'm in the boonies and didn't find anything except a couple of online stores but that's where I get stuff. Fancy Feast is cheaper than most things though; that and Friskies but we've never tried it. Sheba is another one that some like.
If I know my cats will eat the same food over and over, I usually buy from Chewys.com or PetFoodDirect.com. If you buy over a certain dollar amount, you can get free shipping, plus if you set up auto shipping, you get a discount. (you can always go into your account later and cancel the autoship if you want to )
I saw some Purina One canned food at Petsmart. I didn't look at the price when I was there, so I looked online at petsmart.com, and it is 80 cents for a 3 oz. can.
That's weird. I looked for it when I ordered and didn't find it there. Good for you. They do have some nice sales on if there's something you want.
Maybe I'm just looking wrong, but I still only found Purina Pro Plan on Chewy. Wag.com has Purina One but the Petsmart site does have it for .80/can. I hope this helps. It probably would be a good idea to try to add something else to his menu. We can get FF for around .58 normally and sometimes less (you want the Classic varieties).