I have no idea, but I suspect it doesn’t pull from anywhere other than a pre curated set which you can visit at the OS image link above.
Many of the scripts might even not be at github elsewhere at all. And if so it might be worth to think about duplicating for further Zynthian specific integration, compatibility with the available engines instead of sforzando and the controller integration scripts.
Maybe, If the developers here have some spare energy at all besides integrating zynbleton, we could discuss it in an extra space?