I went down to the hardware store, but I could not find anything similar to the part. Finial nuts are abundant, but that washer piece is very hard to find.
I figured out that I have a ready supply of domed metal pieces available from soda cans.
Step 1: Supplies and materials
1. Can opener
3. Drill w/ metal cutting bit
4. Metallic spray paint (that matches the color of your fixture)
5. Scissors or tin snips
6. You may need some protective gloves and glasses
1. Empty soda or beer can
2. Something to spray on (I use scrap plywood)
3. Random wood screw (really doesn't matter what size, but something over and inch)
Step 2: Cutting out the parts
2. Use your scissors to cut the can in half and retrieve your domed aluminum disc.
3. Sand the convex portion of the disc so that the paint will stick to it better
4. Drill a hole through the center of the disc. If you have to hold it, USE GLOVES!!
5. Drive a screw into a piece of plywood and drop you aluminum ring around it. This should hold it into place while spraying.
6. Spray the disc your color of choice.
7. Let the ring dry and place it on your light fixture.