Was wondering if anywhere sold this panel, mines pretty bent on the edges and figured I could just rivet a new one in. Had a look but haven’t found it online.
Try paint man panels. Call them if it’s not listed. I’ve had a few bits from them. Good bunch to deal with. I did my old 90 up and needed that panel too but I ended up buying a whole wing assembly. Bits were hard to find. I’ve replaced that before on a wing but you have to drill out a ton of spot welds then repair all that. Good luck hope you find the part.
Also worth asking SP4x4. I'm pretty sure they manufacture LR wings, so they clearly have that part in house, it's just the only part of the wing they don't list. Probably little demand for it.