Poultry Cell by Rooster Booster is the same, plus it has riboflavin for leg problems. Tractor Supply, Southern States, and Rural King sell them around here, but you can buy them online easily from many stores.
I think you are just not looking in the right location at your TSC. Have you asked the manager? If you can't find PND, you can also use Goat ND. I'll have to do a comparison of rooster booster with PND. Thanks for the info. @Eggcessive