There's still 5nm silicon for sale, but just not at TSCM (the largest semiconductor manufacturer in the world). Companies like Samsung are just now getting around to mass-producing 5nm, and afaik there were a few domestic Chinese manufacturers who claimed to be on the node too.

As for Amazon specifically though, I've got no idea. They're a large enough company that they could buy out an entire fab or foundry if they wanted, AWS makes more than enough money to cover the costs.

Nitpick: it's TSMC, Taiwan Semiconductor Manufacturing Company.

Good catch, my mind always interprets it as Taiwan Semi-Conductor Manufacturer

Yeah, I always need to think twice before writing or saying their name. Same with ASML. I guess there is a reason why TLAs are much more common than FLAs.