Not sure where you live, but I found an auto upholstery supply place. If your in an urban enough area, that will have a good selection. At the other end of the spectrum Pep Boys often stocks Heads Up brand headliner in grey. It's cheap and the color falls within the usual range for the D, but know that it doesn't have the same texture as the factory stuff.

I agree that you'll probably want to do all 4 panels at the same time. the two door panels take a bit of finesse, but they will be easier with the good glue mentioned above. I've heard that a good technique is to get a bag of sand, and once you get the material in place, put the panel inside a trash bag and then fill the depression with sand to help keep the fabric tight to the backing until the glue is fully set. I'd think moist sand would have twice the weight. I haven't tried it however.

Also, when cutting the material, don't underestimate the amount required to wrap up and around the fiberglass, under the outer seals. Its better to leave the material much too long and then trim it after you start fitting it to the car.