You could message Ginger and ask him for it, I imagine he'll have a copy of the BOM somewhere.
Otherwise, you could buy a PMS-PD 2 from
4layertech.com. The PD 2 does the same thing as the internal USB board, but also supports USB-C data transfer and fast charging through the same port. Paired with one of the RVL-PMS boards, it's a complete data transfer, power regulation, and charging solution for portables Wiis. Just add batteries