Is the water coming from around the sunroof into/on the headliner next to the sunroof? I had a leak problem that was actually caused by the stretch window glass channels. There was a gap on all 4 windows (top & bottom), caulked the gaps, cured the leaks.

If it is your sunroof & not another location source, check out this website: Go to the Aftermarket Parts page, do the application survey. You should be able to chat with someone when you figure out which brand you have.

You have not told us who the coachbuilder of your limousine was. It they're still around, you might also try contacting them for ideas.