I don't know if there's an Orchard Supply & Hardware near you, but they carry the two smallest bits (5/32 & 3/16) and have the 5/32 driver bit. The 5/32 fits all of the interior screws. And so far, I haven't found any other size screws other than the 5/32 on my truck.
I've also gotten clutch head bits from Chevys of the '40's and can recommend them highly. Plus they'll send you one of their outstanding catalogs with your order.
