You can order the PICO-56 PCB directly from PCBWay using this link: https://www.pcbway.com/project/shareproject/PICO_56_Retro_Computer_on_a_Pi_Pico_515c59b8.html
To help with ordering components, I've created a Mouser project: https://au.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=8431486f76