You've been warned. I highly suggest you rebuild your own.
I'm not joking. Save the original headliner if at all possible. Those ABS or whatever they make them from plastic jobs don't hold up in the heat from the stories I've heard about. If you crack the styrofoam, you can fix it with duct tape.
It's not super difficult to do the job. You can get it out if you drop all the A-pillar, front/side/rear trim and probably will need new clips for the front and rear as they tend to break upon removal. Side clips you can just push on the trim on the inside, I think, and pull down on the outside of it to pop it free. I can't recall specifically which side works best to push on, but if you break those side clips, it sucks. I think they have repros now, though. Didn't used to. Remove your sun visors and coat hooks, B-pillar trim, and the dome light. Drop the liner down and rotate it as you get it out the door. Again, be careful.
Remove the dead headliner material and take a stiff plastic bristle brush (non-metal bristles) and scrub off the leftover foam. Then lay out your new headliner material over the backboard, and fold it back on itself to reveal half the backboard. Spray the half of the backboard and also the backing of the headliner foam with 3M headliner adhesive spray (this is the best stuff I've ever used). Don't go crazy with it as you don't want it soaking through. Let the two exposed sides get tacky for a couple few minutes. Then reapply the half to stick the glued sides to themselves avoiding any wrinkles as you go. Take your hand (clean) and work the material away from the center smoothing it as you go. Hard to explain, but you don't want to just lay it back like a bedcover. Then after you get that side fixed up, fold the other half over on itself and repeat the process. Once you get the entire thing done, then go back on the back side and make "X" cuts through the big visor holes and where the wiring needs to go through for the dome line. You can use an awl to poke the screw holes for the visors and coat hooks and dome light from the back side. Let it set for a while and to get the stink to air out a bit, then reinstall.
Here's a video of a monte getting a new headliner done. It doesn't cover everything, but gives you a great idea of what to expect. Again, it's just a little time consuming, but it isn't difficult.