I got it from a local fabric store. Not really sure what you would call the material? If you have a local fabric shop, I would just swing in and ask them what material they reccomend for a headliner. You dont want anything too heavy (might cause sagging later, damn gravity) but you don't want anything too thin, the glue might bled through. Good luck.
What type of camo material did you use and where did you buy it from? I want to go the camo route on mine but didnt know if certain types of materials worked better than others. Thanks