The Westerly Debris
The reason why those coast-crossing sources of brilliant light detaching from the Columbia won't be found is that they were almost certainly highly incandescent particles of carbon from the shattered portion of the left wing's RCC leading edge breaking away (see previous OVERTALK posts from a few weeks ago).
In the pre-dawn darkness they would have appeared very bright but soon burnt up almost completely. Anyone familiar with the carbon arc searchlight as used on Maritime Patrol P2's and P3's will explain to you why the carbon feed-rod burns up but punches out over 200 million candle-power in the process. The RCC is made from the same stuff.
So looking for carbon particles that are likely to have been latterly very small would be a vain quest. I would be very surprised if anything is ever found West of Ft Worth.