I signed up just to answer your question, check out https://www.flyscreens.co.nz/.
We live rural and get plagues of flies but not one gets past the chain screen.
They get noisy in the wind when the door is closed so we tie them up.
Ours were about $650 for a 2.1 x 1.5 m doorway, but that includes a powder coated headrail to match the doors, pricey but worth it in summer.
There other online options such as Aliexpress etc.