[Arran]

They are a pretty common item in most decent hardware outlets, they may also have them at Loews or Home Depot, Grainger or McMaster-Carr would definitely have them, and Mouser likely would as well. The new ones may be shinier but they are also not 80-90 years old, I've used them to cover holes some idiot drilled in the back of a Deforest Crosley chassis to add a phono jack and rotary switch, not factory but better then the jagged holes being left there. 
Regards
Arran