The fly screen could work out really well. I also wish to add filters to all my intakes, but just like you say, finding the material is hard. Any close mesh fabric should do, however something like a fly screen, if its a plastic or metal weave will be a lot nicer as it will hold its shape all on its own. Really even just something like tshirt kind of material stretched over a frame would do, which is something I have considered. Just grab an old tshirt, or buy one cheap (like a real cheap, black $5 one), make a wire or metal frame, put hot glue around the edge of the frame, stretch out the material with your hands, and while its stretched lower it onto the hot glue. You will need to hold it there a few seconds while the glue hardens. That should work. Alternatively you could use a very light weight foam. If you take off one of the 5.25" bay covers you will see a very thin, lightweight foam. This would also do the trick.
As for removing the dust filters, there are 2. The first is the bottom one you slide out from the back, reach under and pull. However I assume you know this though and want to remove the front filter. Ill be honest, the front filter is pretty useless, while it will block larger clumps of dust it really does no better than the front grill. Start by pulling of the front panel. Place your hand under the front of the panel in the space between the feet. You will feel a small gap you can wrap your fingers around. It is held in by these funny metal spring type things, all you need to do is pull, both the things that attach the front panel and the part it attaches to are metal, although it may feel like its not meant to come off, as long as you dont bend the front panel's plastic too much it will be fine. Simply pull outwards and slightly up. You will then see that behind the main mesh there is like a thin sheet of plastic/fabric kind of stuff with a hole pattern in it. There are some small tabs holding it in, just place your hand over the span of it, and pinch it slightly and you should be able to get it out, just try not to crease it.
That what you were wanting to know?
i have the same case as u n want to change the filter in the front but i cant find any siutable material. 
). Anyway, its the weekend, I got some time on my hands, perhaps I will give a filter a go for the top filter using t-shirt fabric. I might see if I cant get some kind of magnetic attach/detach kind of thing for easy servicing. If I do ill be sure to post pictures.
