If you ever do get the opportunity to store frozen or live foods I highly suggest it.
I also have a recipe for homemade food that they go nuts over, but it also requires a freezer.
If you feel like ordering online I highly suggest a wide range of repashy super foods (Msjinkzd.com), Kens pellets, or food from angelsplus.com.
Now if you want it form a petstore, I suggest Omega's sinking shrimp pellets as the main base for their food. Combine that with other meaty goodness and your good to go. Whatever you choose. Omega's pellets are a good choice for store bought. Repashy is much better. As long as it contains lots of different varieties of meats you are good to go.
Whatever you do do not feed algae wafers. Even Hikari, known for its quality, consists mainly of grains and wheat. Not only that but corydoras are largely meat eaters. Supplemental algae is a very very poor choice in food for these fish as they are not algae or veggie eating catfish.
A feeding of veggies often doesnt go amiss among pygmies though. A good supplemental feeding of straight veggies every so often is good for their diet. However sinking wafers are not.
Mine go nuts over spinach. I feed a blanched leaf twice a week. Other than that its my homemade food once a day. And a large variety of frozen foods. Not sure what you can find in the freeze dried section. But what I feed is bloodworms, brine shrimp, krill, mosquito larvae, white worms, black worms, vinegar eels, kelp, and the occasional blanched ramshorn snail.
I have just about the healthiest fish I could hope for.
Forgot to add that you may need to cut up the food. They arent very picky eaters, but they do have tiny mouths. My pygmies cannot eat (except the spinach which I put in whole) unless I first grate the food against a tiny grater...