I needed a #6 non metallic washer, and I needed it narrow. Should suffice as a M2.5 washer also.
Easiest thing to do was print one. Original dimensions are: ID: 0.4mm , OD: 5.5mm, Thickness is 0.8mm. If you scale it in Z, you can get it Thicker. If you scale it in X and Y you can make it a #8 washer.