You can buy the tokens at a IEO. If you are asking about if you can buy tokens for cheaper than the IEO price then it's a possibility i guess. But of course. It can only happen P2P. But for me, If that happens, It's more likely that investor is regretting buying those coins because he feels like it's going no where or he's a scammer.
It's not only from IEO but it can be purchased through its own site and when it has been creating a cooperation with 3rd to ran its crowdsale and it can be purchased from there too. that depends on developer and the team whether they wanna try to open a lot of door to purchase the token.