Large amount of Bitcoins 
For an important purchase, you have 2 payment options : cash or bank wire.
Nobody will sell via PayPal, Credit card , or a similar protocol unless you are purchasing less than $500.
From $100-$20000 we can use exchanges like
✔ Bithumb (Average vol $188,044,340 USD per day)
✔Binance (Average vol $1,202,302,799 USD per day)
✔Kucoin(Average vol $30,461,215 USD per day )
✔Bitbank(Average vol $52,241,343 USD per day )
✔HitBTC(Average vol $260,027,928 USD per day)
✔Bitfinex(Average vol $352,119,076 USD per Day )
These are some of the biggest exchanges over the globe.
We can find large numbers of user who are willing to sell and buy in crypto. We just need to keep in mind that if we purchasing large amount of crypto we need to have KYC done from the perspective exchange.
If you want to spend more than this amount you can be a whale in crypto and can manipulate market :-), you need to contact large firms which mine crypto they can provide you the amount you required.
Data collected from Coinmarketcap
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