Tacoma Screw products in Tacoma Washington, USA should have 3-48 screws in stock.
http://www.tacomascrew.com/
Tacoma Screw Products, Inc.
2001 Center St Tacoma Washington USA
(253) 572-3444
I have dealt with them for over 30 years now. Good folks there.
Likely you will not find the screws with black heads or the attached lock washer, but they have surprised me on what they have several times.
Typically the screws come in a container of 50 or 100. They will break containers and sell you just a few also.
Their main store is about 70-80 miles from me.