You can set up a cronjob to sync them, or some have built-in config to do the mirroring [4].
I used Google's mirroring option before. It was fine, but we never had to use it (local copies were sufficient when GH was slow one day).
[1] https://cloud.google.com/source-repositories
[2] https://aws.amazon.com/codecommit/
[3] https://azure.microsoft.com/en-us/services/devops/repos/
[4] https://cloud.google.com/source-repositories/docs/mirroring-...