You mean the cables that connect front panel USB/firewire or audio cables to the motherboard? Doesn't your case already come witih that stuff pre-attached?
Ebay might be your best bet for finding little bits like that, not sure of a particular U.S. online store that sells them, maybe somewhere like maplins
Sheet metal can be obtained at local hardware stores.
Will probably need a rubber hammer and a metal file.
Two piecies of wood and two clamps, for bending the sheet metal.