Does your car have wooden bows built into the roof, or were there metal bows that held the headliner up? In a perfect world, somebody is selling the exact set of bows you need on E-Bay. Unfortunately, that's probably not going to be the case in your situation. The headliner itself is not a problem, there are lots of places to get one on the internet. Here's one place:
www.kanter.com. Your best bet is to call them to order the headliner. The bows can be replaced with new ones made from 8 gauge steel wire, but you have to know how to bend them and how long to make them.