Thanks for the abundance of responses. I'm looking for replacement screws so I match the original narrow slot and head as well as just the thread. Will these vendors have the narrow slot screw heads? I don't want this to look like I just screwed in something that "fit".
No, these would be industry standard size at the hardware. If it is a special gun screw, manufactured by the gun company, sometimes the head and slot will be different. About anyone making Colt replicas will have the same screw.