That is some scary stuff.

Dominion:
You can pick up fixed gear bits at Bikes On Wheels or Urbane Cycle. Urbane will have a larger selection. They definitely have some cheap stuff (they even have a basket of stamped brown steel 17T cogs for like $4 each) but if I were you I wouldn't skimp on one of the most important parts of your drivetrain. Get a decent CNC'ed cog and be happy with it!