There's no special/secret repo that we're sandbagging support for that chip in .. support doesn't exist and you need to adapt Linux kernel drivers for H6 and H616 to the H313 hardware and/or author new drivers for anything missing. There is no guide for how things are done, only prior-art from the Allwinner BSP codebase as an example: mostly an example of how to write low-quality code that needs to be rewritten for upstream frameworks, standards, and acceptance.
We'll be happy to test anything you come up with.