Just as an aside here Oldegreybeard, I've read there has been a change in China. At one time the American importers could order parts as part of their orders, but in order to maintain hours of assembly workers at the factories, the importers now have to order extras of their finished production run products and then take them apart stateside to obtain parts.
It's not just Lionel. Take Williams by Bachmann for example: Many common parts on their website are shown currently as unavailable. Ironically, they do show a lot of shells available for various locos, but those are going to cost you dearly. So for train items that have unique to that product only parts, and in addition, are made in small production runs, long-term availability of parts will continue to be a problem that isn't going to disappear.
For me personally, I stick to train items that are made in much larger quantities and potentially have shared or common parts in them. So for example, if I needed a part for one of my 4-4-2 starter set steam engines and Lionel has it listed as unavailable, there's a good chance a parts dealer will have it stock. In a worse case scenario, I can always buy a second unit to cob for parts. This is one distinct advantage of buying products made in larger numbers, and over a longer time period.
Though as mentioned above, shells have always been one of the more difficult products to get from Lionel.