Permethrin is in Garden and Poultry Dust. It is 0.25% Active ingredient Permethrin. You can find it at the feedstore. I think there are many brandnames. My container says Prozap. Make sure to follow the directions, If you still have questions come back and ask.
There's also some called "Livestock Lice Powder". As Imp pointed out, read the active ingredient.
What are you treating for? If you're treating for lice, be sure to also buy a permethrin spray if you can. That can be "Goat Lice Spray" (read the label - it's less than 10% permethrin), or "10% Permethrin spray". For mites, you have to treat the wood of the coops up to 3 feet on the walls, and then cracks, eyes, joints in the wood. That's where mites live and lay their eggs. You'd treat the birds with the permethrin (not PYrethrin) dust.
On the bedding, scrape it aside and dust the ground. replace the bedding. Then sprinkle the bedding with the dust and stir in. Do so in the nest boxes as well. Buy at least 2 cans. It's cheap but you don't want to run out.
If you can't find the liquid permethrin, buy could buy another can and make a 'paint' out of the dust by mixing it with water or with mineral oil. Make it thin and use that to paint the wood.
Redust birds in 7 days and again in 7 days until you see no more signs of parasites.
I recently found lice on two of my six hens. I dusted all six with garden and poultry powder containing permethrin. I cleaned the coop, run, and nesting boxes and dusted everything. I replaced the bedding and nesting pads. All birds were happy and only had a white powder coating to show for it.
I repeated the whole thing nine days later, with the intention of doing it a third time after another week.
Friday was the second dusting. I hadn't checked on them Saturday or Sunday. The kids found one of the hens dead today. She was laying in the sand hole she dug, which is her normal way of cooling off. There are no obvious signs of trauma and I never saw lice on her. They are only about six or seven months old. She had a short broody spell a month ago for about a week. That's it.