A very good mail-order source is:

  McFeeley's Square Drive Screws          (800) 443-7937
  712 12th Street                         (804) 847-7136 - FAX
  P.O. Box 3
  Lynchburg VA 24505-0003

They stock all sizes of screws, in brass, stainless and other materials
as well as drivers.  Prices are good relative to the Home Depot.

Roger Wiegand