My roommate works at a hardware store so that puts me at a huge advantage for DIY projects...Id be lost otherwise. Check other local places, lighting companies, hardware stores, grocery stores...I tried looking online for ya but all I came up with was this creepy picture...
Lowes or Home Depot. It's with the ceiling panels and costs around $12 for a 2x4 sheet. If you ask for help, ask where the ceiling panels are as eggcrate will have no meaning to them.