[Arran]

 I'm not sure about model 90s but some of the model 70s used Sprague filter caps from the factory, if those are not aluminum they are plated with something to make them a silver colour. If push comes to shove, and you really want copper filter cans, you can make some fake Mershons out of a selection of plumbing parts, a short length of copper pipe of the appropriate diameter, a matching pipe cap, and either a brass or plastic threaded nipple for the base.
Regards
Arran