5 1/4 inch bay cover with mesh/filter for intake purposes?

"Lian Li has this for their cases:

FrozenCPU sells a black and a silver version for around USD 10 each. Same with Performance-PCs.

Coolermaster sells something similar for their cases - here's one in the US, a different one in Europe - though you'll have to see if they can snap fit your case. Looks kind of proprietary.

NZXT has a standard looking one for their cases, but I can't find a parts vendor for just that one thing."

"I've done three things in the past:

Just pop the covers off and leave the hole there and open. Not pretty but it works.
Pop the cover out and take a Dremel tool and fashion one yourself. I used a Dremel, some metal mesh, and some crazy glue gel. The thing held up for years before I finally threw the computer away.
Cut a nice fine hole in the SIDE of your case and put an 80mm x 80mm fan (or whatever size you choose) in there. You can find a ton of places on the internet where people have ""modded"" their cases like this. You may wish to test mounting the fan blowing both IN and OUT to see what is more effective in your particular case.

I suppose I could also mention ""the obvious"". If you don't want to wase time ""modding"" the case and you don't want an ugly ""hole"" in the front... a few bucks will buy you a new case. Sometimes throwing money at a problem IS the most efficient option."