I have never found one in a store,. I live in Louisiana, and always had to buy mine online,.. but I don't even do that anymore,
I buy a human herbal de-wormer in capsules. I mix 4-5 of them per gallon of water and give it for 3 days making a new mix for each day.
I use a de-wormer with wormwood, walnut shells, garlic, pumpkin, fennel, clove and flax seed, and some other herbs.. We have been using it for 2 1/2 yrs on a free range flock,. checked and checked closely,...no worms.
I do have to say we also use DE in the feed a couple of times a year and in the fall raw pumpkin seeds.
I feed plain organic yogurt and put ACV in the water after the de-worming to put friendly bacteria back in their system.
I know that many folks say natural doesn't work,.. but it does for us.
Hope this helps.