Hi,
Here’s a [https://www.head-fi.org/threads/koss-esp6-refurbished-vintage-electrostatics.234504/|link] that may be of some help to start with.
Any reputable professional electronics repair service, especially those into audio repairs, would most probably be able to get the headphones working again. The electronic components, if faulty would most probably be replaceable except perhaps for the speaker cone itself if it were damaged.
As for refurbishing them back to original look, that may be more problematic as they haven’t been supported by the manufacturer since 1973 so getting replacement parts will be difficult if not impossible especially if they are the more “cosmetic” parts i.e. any exterior components e.g. earcup, exact headband etc.
You can only try and see if it can be repaired.