I've got one for my 93 cube that I'm not using now that I put a full canopy over it. You can buy it, cut it down to fit your tank. It's an easy job! PM me if interested.
You can order the mesh from Bulk Reef Supplies. I couldn't find it locally, or online anywhere else in less than 50 foot rolls. The frame parts can be purchased from Lowes or Home Depot.
When I did mine Acroholic shipped the mesh out and I got it in a day. With the parts from Ace hardware I was able to build two that were 16-1/2" square for less than $25.00. I could only find the .140 spline at Ace but I think the .125 from HD would work.