Here are two links to detailed discussions about treating ponds with suspended clay. There are several possible treatments. You might read a bit to determine which treatment is optimal for your pond, and which has the best cost/benefit analysis for what is available in your area.

Alum Kicks Clay's Butt

Part 2

Once you know the exact description of what you need, you can find a supplier in your area.

Good luck on getting your pond water cleaned up. The fact that your sample cleaned up nicely is a very encouraging result.