How to find a symbol master by name?
I'm trying to write a plugin that will set overrides in symbol instances in specific layer groups based on data from a JSON file.

The first problem is that overrides in a symbol instance don't have any name or label, it looks like I can only reference them by index in overrides array. I figured out that maybe I could get these names from the symbol master. However, I can't figure out how to get an existing symbol master. The API only mentions how to create one, not how to find one.