I could just give you some if you make it out to my house. Have a big piece that used to be over the shade house that I'm just throwing away. Of course it has huge holes in it, but it doesn't sound like you need a lot...
Large plant nurseries usually have shade cloth by the foot.
Are you trying to block light from outside or from the lights?
I have seen people use a piece of plexi glass and paint it white to dim the lights a bit. Not sure what paint they used. You can also get white plexi glass. Just a thought.