I have a Gateway Emachines T6412 that is missing the case cover. The dimensions of these machines are: 14.25"H x 7.25"W x 16.00"D This particular machine (and I would guess many other emachines) has a two part case cover, one part is the side panel for easy access to your hard-drive cage, which is removable after one screw. It's a very nice way to package a computer. The other part of the case cover covers the opposite side and the top of the computer. I have no idea what I did with the case cover. In the past, I have used plywood and made my own but it is so tedious to do that. Any help or ideas appreciated.
I think you're going to find it hard to get a replacement, due to the age of the machine (2005), even a quick look on Ebay turned up no results.
It's funny - as of two years or so ago, I bought 2 used T6412's in the same week. I still hold hope that one day someone out there in PC land will want to pitch their entire T6412!