I've had positive experiences with the Colt's polymer lock-washers. A set is very reasonably priced and comes with two different sized washers to include the hammer screw as well as all the frame, trigger, and bolt screws. I've always gotten them directly from Colt's.
I've read several times on the intewebs that these washers don't work well. But, to the contrary, my experience with them has been that they hold screws well. They are not, however, perpetually reusable. But, again, they're not expensive.
I remember in the '60s that Roooooger boasted they assembled their six-guns with "nylock" washers. I've never used such washers on Rooogers, but assemble all my Colt's and clone pistols with them consistently.
I'm pretty sure I have a loose screw, but it's not on my pistols!