i bought a product called enviro-fly from the hardware store here - perhaps you can find something similar. it's a plastic tube about the size of a drink bottle, with holes at the top and a yellow lid with a hook. it comes with a sachet of powder i mix with a cup of water, then hang it in the run where the chooks can't get at it. it attracts flies and then they cant escape. replace the sachet and water every 2 weeks. kinda gross to look at but very effective. i use DE too. i have a sand floor in the run which is small enough for me to scoop the poop each day. all this helps, but it wont stop them completely.
good luck - hope you can find something like this product to help