Like doda stated, go to your local hardware store. However, go to the plumbing department. They should have a large selection of RUBBER washers. I found just the right size and use them on my Beretta 686 Silver Pigeon.
Machined aluminum AN washers as used on aircraft and race cars to align nuts for cotter pins. Available in 1/16 an 1/32 inch. Attractive color. Get them from Aircraft Spruce & Supply...available in aluminum, stainless and nylon. Bore sizes in 1/16th inch increments from 1/8" to 7/8".
THANKS a ton Tron! , and everybody else. I never thought of finding what I need at a hardware store, just thinking of ordinary washers there. I live so close to a Lowes and Home Depot I wouldn't even trouble you Tron, but I appreciate it! They aren't 4 minutes away.
Ken: As someone mentioned, get the nylon/plastic type washers. They come in different thicknesses, so you can experiment with the adjustments. I got mine at the neighborhood ACE hardware. I believe they come in white and black. Ed