Before any time and money are spent on the covers you mention, may I suggest a thorough check of the wiring inside the lamp? I have seen many electrical devices from the 1950's to the 1970's with cracked, fossilized, or softened insulation on the wires, and disintegrating switches and plugs. This is of course very dangerous if the conductors should become exposed and contact the user or the metal frame. Just urging caution with old electrical stuff. Sorry I have no idea where you could get covers other than to maybe have someone measure the existing ones (or measure where they fitted if they are missing) then model them in CAD and 3D print them in PETG or ABS.