Make it. For the congealed variety, it's dark karo syrup. For the runny variety, it's murphy's oil soap. An ounce of Red #40 and a drop of Blue.
Otherwise, go to Lynch's in Warren or Dearborn, Screamers in Roseville or Pegasus Theatrical in Southfield. Any good costume shop has it if you don't want to make it. Mehron, Ben Nye and Graftobian all sell it through their website.
I'm planning to NOT attend this event. I less than slash three'd prom the first time round.