HI Si Chen,
SAM's utility rate calculator is in the utilityrate5 compute module of SSC. It was written specifically for SAM, and is not based on a different project.
You could use the SDK (or PySAM) to run the utilityrate5 module as a standalone component, as long as you can set values of all of the input variables correctly.
The instructions on the SDK page should provide resource to help you learn how to do this:
sam.nrel.gov/software-development-kit-sdk.html
If you try that approach and have questions, please feel free to follow up!
Best regards,
Paul.