Would it have been possible for someone to have bought/acquire like 333,333 bitcoins in march of 2010?
Indeed, 333,333/50 = 6,666.66 say 6,667 blocks,
that block was mined on 2009-03-07, so long before march 2010 there was that much
, in march 2010 mined already.
The first block that was mined in march of 2010 was block 43085, there was already 2,154,200
BTC in circulation right before march 2010 started.