There is a 5,000/hour rate limit. (https://developer.github.com/v3/activity/starring/) So 120,000 repo Stars a day at maximum utility.

You can get a list of all GitHub repos and derive their IDs with some BigQuery shenanigans on the GitHub Archive, then just feed the IDs into a while-loop. Simple to implement, albeit not necessarily ethical.

EDIT: 5,000 limit is not endpoint specific. But if you use it all for one endpoint...