My wagon has the third row seats that i plan to use once in a while, but i now believe the seatbelts are missing? Ive got the buckles that are attached to the 3rd seat, but the belts seem to be missing. there seems to be something removed from the ceiling on both sides, would thatve been them? would i be able to replace them with others? thanks.

on my wagon the places by the ceiling you are referring to are the 'loops' that guide the belt through, for the over-the-shoulder belts to the rear seats.
not to the third seat that faces backward.
as i remember all the belts are contained in that fold out seat in the rear bed above the fuel tank.
maybe they got pushed behind the fold out seat?

I just installed a used third-row seat in my 90 240dl wagon, which had never had a third-row seat. There are lots of pre-drilled holes to facilitate the installation of another seat. Two of those holes are in the rear area above the windows, and forward from the bar that holds the second-row shoulder buckles. That is where the upper fastener for the third-row shoulder belts is located. In my car, they were behind the headliner, but I was able to feel them and cut through to assemble my seats. I had to drill through the wheel well to attach the lower end of the buckles. I'm not sure if that was the right thing to do, but I couldn't find a pre-drilled hole for those. The project went well, and I can now carry the wife, four kids and a dog comfortably. If you're missing the belt, you might find something at IPD or ebay, but you also might end up building something for yourself. Use the holes that are already there and attach something from a junkyard if you have to. Seatbelts are cheap there. Good luck!