Where can I find these on D&D Beyond or otherwise?
They are not available, from the DnD Beyond Forum, as per 15 June 2019:
DDB currently doesn't have a means to copy character sheets from one user to another. Without this framework, they have no way of providing access to pre-gens; it's the same for the starter kit.
Intra-user copying is coming, and with it will come access to pregen characters.