Hi David;
Yes, people have been making their own. There’s a Facebook site titled “Piper Arrow (pa-28R) and Cherokee (pa28) owners. You might find a source there.
I’ve seen posts from folks that making them and selling them, but heard that the FAA is not amused.
The AD says that the inspection can be done with a borescope, through the openings covered by the wing root fairings but the catch is that the AD specifies a borescope with a 10 x magnifier.
Those are expensive.
Some owners have pulled the fuel tanks to get access; this works pretty well if the area to be inspected is clean, but if that area is covered up with dirt, grime, and other crud, it would be hard to guarantee there’s no corrosion down there (esp. aft side of spar) without the inspection panel. The AD must be competed with in 100 hours time in service, or 12 months from December 28,2020 so you have some time to find an inspection panel.
