I would recommend getting a residual spray as it lasts for up to 2 months. In Canada we can't get any permethrin powder legally and carbaryl has been banned.
We CAN purchase something called Doktor Doom residual spray and it works well in the coop It's about $23/can 450mls..
Spray all perches cracks and crevices in your barn and get an ivermectin Injectable from the vet. Put 3 mls in a gallon (4 litres) of water for 2 days. If they drink it all give fresh water for the remainder of the day. On day 3 give another dose of 3 ml in 1 gallon of water. I have 80 plus chickens. I gave them 3 gallons and 9mls of ivermectin on day 1 through day 2 then gave them the same amount 3 gallons with 9mls on day 3. I gave them fresh water only on day 4. I repeated this 10 days later. This was per my vet. He said there's no need for withdrawal in his opinion as people are given ivermectin for worms, but I had a 7 day egg withdrawal anyway.
If you have a manageable amount of chickens you can use the Injectable ivermectin as a topical or oral Use point 1 ml (that's .1ml not 10 mls) and put in their mouth or on the back of the neck or near the vent.
Repeat 10 days later. If the infestation is still there try a 3rd time to break the cycle.
Hope this helps. And I feel for you. I'm just starting to see the benefits now.
On a different note, you may ask a pest control company about doing a spray for you with permethrin. It may be cheaper (cost me $200 in cans of spray and a sore hand after 2 days as my barn was big) and faster.
Spirit
Greeter
Friend
