What's a good way to patch missing covers on my computer case?

Before you guys make assumptions, I'm not talking about covering air vents.

I'm using a very old ATX case that I updated with some of the latest hardware. But my case is missing some covers like a cover for the expansion slot and PCI Express slots. This could potentially disrupt the air flow the case intended it to use for.

I may have misplaced it (its been years since I uncovered the thing, gimme a break) and I finding certain parts for this case would be hard to find. So what can I do to cover it?

My computer specs, in case if relevant:

• Asus A7V600-X Barebone Kit / ATX Mid-Tower Case (Back in 2005)

• Asus P68Z68-LX Motherboard

• Intel i5 2500k

• 550w PSU diablotek

• 1TB Seagate 7200rpm SATA 6/gbs

Here's some pics for what I'm dealing with.

• Back

• Front

I don't plan to buy another computer case.