The sear doesn't take all that much to sharpen, I've done it on mine. Have one that has a real light trigger-the trigger spring , the little one up front under the button, is clipped with fingernail clippers. This is actually the best trigger I've got. The problem with doing that is if you cut too much off the spring, it ceases to work.
By sear, I'm guessing you mean the little triangle wedge that goes to the hook on the back of the trigger. We use just a little emery cloth-or like you suggested, a stone-to sharpen the underside of the little hook and the point of the sear(by sharpening the angle, or taking down the angle). I have had one sear that had a factory groove down it, I took it out.
You aren't the only one to lose a spring, first time I took the trigger assembly apart, I shot that little brass trigger spring off the ceiling, off the wall, across the room, etc. I think it bounced 3 or 4 times. There I was, down on the floor, with a flashlight. When I gave up, there it was, at my feet! It made it all the way around the room back to me!
