I managed to get my hands on a Denso VS-6354CM, RC3-V6A controller, and teach pendant for less than $400 from an industrial surplus supplier. It has the normal issues (dead encoder batteries, dead controller battery, missing cables, setc.) but I'm making great progress forward. The J6 motor was fragged, but I found an original replacement on eBay relatively cheaply. I've also been able to purchase the full set of cables (including the IO cables) with the exception of the motor power and teach pendant cables, but I found the correct connectors, bulk cable, and pinouts to make my own.
My main challenge now is getting the parameter set to restore the controller. I have a lead on this, so I'm really hoping it pans out. I do not have the floppy drive so I am not sure how exactly the restore will work. Maybe the values can be keyed in from the teach pendant, or perhaps I can make a generic floppy drive talk with this unit. I have a backup option to convert the entire system over to Allen Bradley servo drives and PLC to do robot kinematics.
I wanted to start this thread as a place to ask questions if I get stuck and to share manuals. Denso support has been extremely kind to me and is providing a lot of information and help, even though this robot is out of service.
Attached the service manual to this post.