dragonboard 820c is base on the Qualcomm Snapdragon 820E chipset and available for sale though Arrow.com: https://www.arrow.com/en/products/dragonboard820c/arrow-development-tools
As mentioned in a few places, the dragonboard 820c is an upcoming board from Arrow, based on Qualcomm Snapdragon 820 that follows the 96boards specifications (extended size flavor). While the board is not officially launched yet, a beta version / prototype is available to some developers, including developers at Linaro.
This forum can be used for any support question related to the beta version of the board. A lot development is happening for this board/SoC in the relevant upstream communities and users are very much encouraged to join these efforts!
Please note that there is no formal/official release available for dragonboard 820c Beta yet, and that the proprietary firmware are also not publicly available on Qualcomm Developer Network (QDN).
For more information about how to get started with Linux on this board, please check this out: https://github.com/96boards/documentation/wiki/dragonboard-820c-Getting-Started-With-Linux.