There's the collected which is bloody hard to find. Then theres the orginals. The epic isn't bad.
2)The Fishwrap - Special Edition one - black and white
3)The Epic - Special Color collection -
4)The Comico - Freelance police special - when they on the road
5)The Epic - On the moon one.
Then there's all these small appearances everywhere which i'm too lazy to mention.
The comic store here in Toronto has TONS of Oni Double features which has the Skeptical Invesitgators comic in it.