I want to buy their stocks.
There are two ways to buy asicminer shares.
One is to find someone who owns asicminer shares and buy them off them. These shares are not listed on any exchange, so all transfers are done privately (with ownership tracked by the management of asicminer, represented by friedcat here on the forums).
The other way is to buy Passthrough (PT) shares on one of the exchanges. Bitfunder and BTC-TC are two exchanges I know of that host asicminer PTs. A PT holds shares in asicminer and then lists those shares on the exchange 1 for 1 (or in the case of the PT I'm planning on launching, 1 for 100). A PT normally charges a small fee on dividends before passing them on (usually less than 5%).