If you don't want to use the default (free) Microsoft/Office 365 group connector then you can use the Microsoft 365 Group APIs (using Microsoft Graph) in Power Automate (premium connectors required).
You can get the member of M365 group members using API like:
You can learn more about how to work with M365 Group APIs at: Fetch Office 365 Groups Programmatically Using Microsoft Graph API
And how to work with Microsoft graph in Power Automate at: Calling Graph API From Power Automate Flow.
I am not sure about all your requirements, But if you can achieve what you want using free M365 group connector then I will suggest to use that only because using premium connector will add more cost to your solution.