As a general rule, no one who is really trying to buy a huge amount of some crypto will ever want you to know that in advance. Up until the point when they have completed buying, they will probably be silent, or even talking it down, creating FUD, etc, to try and induce people to sell to them.
Anyone claiming they are going to buy 100s of BTC worth has already bought and just wants you to buy. And if its actually true, then they bought 900 btc already, and have 100 btc to go, and simply want people to join them in buying and help drive it up.