This is an archive of schematics for boards that ArduPilot supports. Note that ArduPilot supports many more boards than we have schematics for here, but this archive covers some of the best known boards to help with ArduPilot development
Also note that pinouts for all boards supported by the ChibiOS port of ArduPilot usually can be found here: https://github.com/ArduPilot/ardupilot/tree/master/libraries/AP_HAL_ChibiOS/hwdef
Be sure to adhere to the license terms of the OEM providing the schematics. License terms are usually found in each OEMs schematic folders. At a minimum, this usually requires attribution to the OEM and/or inclusion of the licensing language.