
I have not found a specific cable that fits the iSight mounting clips because I use the standard Apple cable.
Any Firewire Cable vendors that will guarantee that their extension cables are compatible with and will not cause damage to your iSight can be a potential source for you. Some of them may already have an available "thin" end for their cable that will work for your application.
If you already have a favorite vendor, you can ask for his help. If not, you can check with any of the vendors listed in the various links from this
iSight Discussions search for "firewire extension cable" (without the quotation marks.)