You could script it with a headless browser and Playwright, probably, or just inspect the NotebookLM app and make similar API calls to the ones it's sending.
you can try outscale.ai (disclaimer: i'm the founder). if you like, we can work on providing you an api
You can use https://www.vadoo.tv/notebooklm-podcast-generator which is an alternative to NotebookLM and has api