If you are looking for something of an exact size, then take a look at laser master ( http://www.lasermaster.co.uk/metal-laser-cutting ) If you select washer in the cutting type, and specify a inner and outer diameter, it will give you an instant price. I have used them for small custom aluminium washers in the past. They take a while to come - guess it depends on what material and thickness they are cutting on the day to make a batch job up. They custom cut mild steel up to 15mm thick and stainless 304 up to 10mm. It will cost a little more than a disk brake - but you can get exactly the size you want. Hope this helps John