Yes, the slot covers are stock, and yes, I have a few, but not 12; you can buy new ones on line, just make sure they are sturdy (in case you re-task them to become VGA/DVI/USB socket holders -- Dremel is your friend). The A3000D slot-holders are not stock but might be repairable or a hardware store (Lowes) will sell sheet metal for fabrication of a new one. Easy if you have access to the folding and cutting tool (machine shop); not so easy using tin snips, anvils, vice grips, and such. Pick up metric M3 & M4 screws you will need to use on the cases.
A3000's are a bitch :-) to work on. I'm in the process of selling my last refurbed one and the "other one" as parts -- working parts, just won't work together.
