The previous poster appears to be referring to a common misconception regarding US law regarding automakers -- but there is actually no such requirement, even for them, and certainly not for bikemakers.
And furthermore, due to a few ten million people voting last fall to destroy the United States, even if there was such a law, it would be as meaningless as the rest of our laws currently are.
If the item has a warranty, they have to be able to make good on that warranty by either offering the part, a suitable replacement or a refund. Which I believe is US law, but doesn't apply to non-warranty situations.
This isn't a warranty, but it is the kind of thing that I think consumers should take up with manufacturers when they create this sort of bottleneck. 3T got people to buy a certain gearing set up that only works because of their proprietary 9t cog, and then they bail and you now have this very silly chainring pairing.