I want to build a system around a Ryzen 7 2800H but I can not find any place selling this chip. It has been almost 8 months since it has been announced.
The 2800H is a mobile processor, so you won't be able to buy it unless you are a notebook OEM.
BlackZion is correct. That Processor is considered to be a OEM/TRAY Processor according to CPU World:
Definition of OEM/TRAY:
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