I can't help on finding parts because have only had my T4R a few months, but I can suggest something for perhaps retrieving your part. A month ago I replaced my map light panel with one from eBAy so that I added HomeLink. When I pulled down my old console, one of those nasty clips went spronggg, flew off inside the roof. Sounds like same happened to you. Could not get it back through the hole it clips into. But I noticed that the holes above the sun visor clips are larger. So I pulled down the passenger side clip, used one of those cheap little telescopic magnet things, held my tongue just right, cussed for a while, and finally got the clip out of roof.
One other consideration - if you are talking about same clip - that is not something you want to leave up inside the roof - it will eventually get to a position where it rattles. Worse yet would be to contact back of map lights, sunroof switch, HomeLink if you have that - could short something up there.
Now if you are really stuck, I kept my old panel, it has one good clip, the one that flew off is sort of distorted. PM me if you want one in an envelope to you.
Hope this helps