Shown here, these have a woofer from Volt, used in PMC speakers.
http://manskerconsulting.com/audio/index.html
Look on the back of the frame for the EIA manufacturer code. Then, contact some speaker repair shops and let them know all of the numbers in the back of the frame. If you can, e-mail come photos to them.
Thanks Hi-Fi. I have never heard of Nelson Reed before. I see they are long out of business. They were in California I note. So it is possible Orange County speaker repair may know something about these speakers.
The speaker in question is over 20 Years old and a passive sub with a 120 Hz crossover and equalization. So the OP will need an exact replacement.
Volt used to have an American agent back then in California. I think I have an old catalog of theirs, and just might be able to find the spec of that driver. However I doubt anything comparable is made to day, and the chance of getting even a proximate match is remote.
I see the speaker has a 3 amp fuse. The OP should check that that is not blown.
Volt are still in business. So the OP should definitely contact them. It is possible they still have parts available to rebuild these speakers.
The other possibility is that
Wilmslow Audio, who have handled Volt driver sales in the UK for as long as I can remember, may have parts.
The OPs driver is not among Volt's current offerings.
His sub is actually a sub that matches to another NR speaker to make a three way system.
By the look of the design and specs, this system would be seriously out classed by more modern designs. In as much as these speakers seem to have been well regarded in their day, I don't think they are worth a lot of expense and trouble to repair them, unless this is a collection/museum situation. Even then I think the hill will be steep and impossible if a reconing kit is NLA.
