Not much obsidian where I live, either, so I chose a different approach:

The handle is a hickory sledge hammer handle, about 3 feet long. The blades are called "knife sections" and come from a swather (for those who don't know it's a piece of farm equipment used for cutting hay in a field).
They are triangular shaped, so I cut the tips off with a surface grinder. I also notched the sides of the handle with the grinder, inserted the blades, and used Liquid Nails glue to hold them in. It's pretty stout. I've buried it the entire width of the blades in a stump before.
The blades are fairly easy to find at a farm implement store, if you can find one in your area. They are about 3 inches to a side.