If there are others like me who struggle to find the latest link for the project, as previous one goes 404, it is:
https://github.com/MikalDev/c3_spine_plugin
also I wonder if you will support this with new SDK, thanks for your effort Mikal <3
I probably will update over time, what are the new SDK features and version number you are looking for (so I can think about how to implement in plugin)