All naturally formed landforms (e.g. reefs, cays, banks) in those areas is already the territory of a country, with no terra nullius remaining, although there are a couple disputed claims. You want to search for the phrase "buy [country name] islands".

Crazy what people will do for IPv4 space these days

If you had a carrier strike group in the area, you could try (after the example of https://en.wikipedia.org/wiki/William_Walker_(filibuster)) getting your islands for the iron price?

Tell me more. How would this be implemented in 2026, for science thought experiment.

This works like "price upon request"; if you have to ask how (much), well: it's not for all.