Where is HackCo? - A startup idea that leverages the part-time hacker community

Well, for starters, I'm not quite sure you would want to call it HackCo. The typical client is not going to have a good conversation with their director about hiring a company that calls themselves HackCo. The perception of the term "hackers" for most people still describes the cracking community, as inaccurate as that is.

That being said, there are a more than a few programming guilds around that are available for contract work. For instance, look at all the teams on eLance. They may not all be open-source but I'm sure quite many are.