Through the website (it's on the front page), blogs, blabbermouth, and other random websites. I'm sure there are a number of people here who lurk on the forums and don't have accounts, too.
I'm getting 4 so that two of the people coming with me who are over 18, won't miss out on it, and one for my mom who is a huge metalhead and power/prog metal fan.
We have averaged about 100 people on Wed night the past two years. I figure that 90% of them are forum regulars. If we sell 125 tickets on Saturday (or by Monday morning), then I'll go ahead and announce things. I simply have to wait on confirmation from the venue on sales.