Alan,Sorry about the empty post. I started to write on my phone, and my wife needed me.
I'm surprised that nobody suggested this, even though all the previous suggestions were helpful.
Have you looked into reedless accordions? There are some that might offer temporary help until your shoulder can support your current accordion, and most are lighter than their reeded cousins. In looking at reedless, I would rule out those without built-in speakers, because you don't need the additional burden of carrying around an amplifier. Of course, if you are playing for large audiences in large halls, the internal speakers might not provide enough volume, but most reedless models have audio-out jacks so you can connect to the house PA system, perhaps even wirelessly. The additional bonus is that most reedless accordions also have MIDI built in, so you can use the accordion to control another MIDI-equipped sound source.
The biggest hurdle to overcome with reedless accordions is bellows response and feel, but a few hours with the instrument will solve that problem.
Good luck to you whatever you choose.
Please can you give an example of a reedless accordion as I have never heard of them. Maybe if there's one on ebay for example.