Unable to get eventsources list using REST API

Can you provide some example code? They fact that your getting html response instead of JSON likely means something more fundamental is an issue then the specific EventSource API details. You might want to use some of the REST v1 examples on the support pages, to make sure any API calls work, then you can convert them to v2 convention.

Based on the v2 docs, it does look like import via XML is the documented method to create EventSources. You might need to generate the XML file (perhaps by having an XML template that the script modifies) to provide into the API call.