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, block was mined on 2009-03-07, so long before march 2010 there was that much, in march 2010.
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.