|Your best bet is to take it to a computer shop and see if they have anything that matches. Usually they'll have a box in the back where they've been tossing leftovers when doing upgrades.|
If that doesn't work out you can get something like a wood shim from a hardware store and make your own rails.
Does the case have any rails? If so take some good pics and post them. I might have some.
For the missing bezel covers, I've installed an extra cd or floppy drive just to fill the hole.