I bought it new from volvoworld.com (I think). They used to advertise here. I'll try to find my invoice, but the part is the "interior dome light kit", and it came with the replacement switch for the dome control and for each of the map lights already installed on the switch cover. It's part # 9178327-4 for 93-2000 without the sunroof and part # 9178326-6 with the sunroof. The part is $56.88 without the sunroof and $59.36 with the sunroof.

These are new original Volvo parts . But since the dome lights weren't working at all (except for if I held in the light, which you can't exactly do when loading the family into the car), it was well worth it. Took about 10 minutes max, but make sure that you have a T-10 sized torx bit to remove the 2 screws that hold the cover in. I had to go to Home Depot to get one because I didn't have one that small. Good luck.