I would think that's the case on this "rocker panel striker" sadly out of production!... but on the other hand, why would they limit a production piece that was produced
for the dodge ram quad cab that was introduced in 1998 and ended in 2002?.....that's 5 years of production...but I get your point, because Dodge does not stock this
item anywhere in their book of inventory parts.........So Determined to find one though!!
Look at it from this perspective. You produce a car, you only need whats on the BOM to build the car, you don't need extra parts on the car, just a little overstock in the factory in case some are dropped or messed up or something. Then you only need a small number of certain parts after production is stopped to account for repairs. This is a rarely problem item during the lifespan of the vehicle, they may only need one per hundred trucks within the timeframe the vehicle is expected to fail, so they only produce that many over once production stops. Once they run out, it is expected that most all of those trucks will be off the road. I don't think they expected people to keep fixing them for so long since the 80s and 90s was really when they stepped up planned obsolescence in cars. They perfected it in the early 2000s.
Now, its way past the life expectancy of these trucks so their stockpile of parts designed to replace broken items is scarce in favor of stocking parts for Gen3 and even Gen 4 trucks. Had your issue been with something that more often breaks, replacement would be easy as there would have been sufficient demand during the lifespan of the truck for aftermarket manufacturers to step in. For example, headlamp switches or light housings, window switches, etc. Those are still easily available from aftermarket suppliers because they made or bought equipment to manufacture that specific part. To a manufacturer, to produce the striker for the rear door (of which only a percentage of trucks had vs the stud for the front door that all trucks had) is a waste of resources as the demand may be as low as 100 per year, out of millions of trucks on the road. They are better off spending resources on a part that has higher demand.
I'm going to guess you will never find a new one, ever. All you can do is pull one from a junker and sandblast then paint it, or goto a body shop and see if they have any that would fit (probably only if you have them do the labor of putting it on).