I think some of the old CADEX hanger/dropouts are getting tough to source, but they fall into a very unique niche, and probably are part of the question above...

Generics (Pacific Cycles for example) are very ubiquitous, and should be available for a good long time. On the other hand, big name brands might introduce one for a couple of years, the move on.

On the bright side, many replacement hangers are not OEM, but rather copies. And, long as Wheels Manufacturing and similar companies have the CNC templates, they'll likely to continue to support them.