Just need a screen for my six inch fan..help!

I had a bug problem last time and I'm trying to prevent it this time. I am pulling air out of the room and into the attic via a six inch hole in the ceiling... the fan is actually in the attic and just sits nicely in the 6 inch hole. Today I went to Home Depot to see if I couldn't find some sort of screen to put over the top of the fan so bugs can't try to call into my garden - no luck...didn't see anything that would have done the job. Do you guys know of anywhere that carries a product like this? It's probably unlikely that the bugs will crawl through that six inch hole considering tons of air is usually flowing through it, but I'd like to be safe.

Well I have a screened in porch, and I have had to replace it several times due to my dogs, and I just buy big rolls of screen at home depot. Maybe a little more than you need, but is that the type thing your looking for?

i would just use some speaker cloth