Where to buy huge amounts of Bitcoin? I read the following article: 


Bitcoin surging higher after mystery trader buys $344mn in cryptocurrency, Russia Today, February 19, 2018.


Where could the man buy such a large amount of Bitcoin? On an exchange?
Such amounts will not be bought in a single transaction. Instead buying them will be spread out across different exchanges and different periods of time. If this is not done such a transaction would buy up the whole sell order book of an exchange and would run up the price through the roof.

A total of 34k bitcoins is about 3.6% of the volume of the bitcoin market in the last 24 hours. Your Russian friend is a whale by any definition for sure, but 34k bitcoin is not an impossible amount to buy.