Hallo guys!
As the title says, I'm looking for some obsidian. I'd gladly barter lead glans, half truck spring or some leather for it.
If you've what I seek and are interested in trading, just let me know 
Greetings,
Mauro.

Would any type of rock with a good hardness and concoidal fracture work? If so you might want to expand to flint.
But! If you REALLY want some nice obsidian, try finding the GREEN variety that only comes from the jungles of central America! That stuff is awesome! I believe it was first mined either by the Aztecs (who were skilled slingers as a side note!) or the Taltecs (not sure if I spelled that right) for use in blade making. They believed the green obsidian was better for some reason...?

Glass is glass.  The edge is going to be the same thickness (19 microns or so), the colors are way different.  There is Rainbow sheen, that in the right light looks like the sheen of oil on water.  There is pumpkin, mahogony, midnight lace, which looks black until you hold it up to the light, then you can see clear spots that look like lace in the black background.   Usually though, the more colors a piece has, the more brittle the overall blade will be.

There are a number of dealers who specialize in obsidion, Craif Ratzat is probably one of the best known, if you can catch him at home.

Thanks Johnny but I've found some obsidian!
Many thanks anyway!
Greetings,
Mauro.