Where to find black egcrate?

[Delphinus]

Check with a lighting supplier. Something like Litemore or BriteLite or wherever. You don't need to order it from the U.S. the lighting stores will have it. However expect to spend about $15 per sheet. It's way expensive. Krylon Fusion black paint has been used to make eggcrate black for many people and it's totally fine to do it that way.