July 2020, and so far still no tuners that are affordable by mere mortals. If you really must have something right now, there is the TVXplorer bundle from RedZoneReceiver.tv -- it includes an ATSC 3.0 dongle for your laptop, the associated software, and a few accessories. It costs $2,300. I don't think it makes much sense to buy one unless you are one of the TV stations testing out broadcasts and need something to receive them.
A few high end TVs have ATSC 3.0 tuners built in. They include some of LG's 2020 line of OLED TVs (but not the relatively affordable BX and CX models), top of the line OLED TVs from Sony, and Samsung's 8K TVs.
But that will change soon. Silicon Dust will be shipping the HD HomeRun Quatro 4K, which includes two ATSC 3.0 tuners. (The other two only receive ATSC 1.0.) Shipments to Kickstarter supporters were supposed to begin this month, but were delayed by a problem with the first 1000 units that the company received. First shipments are now scheduled for August. The Kickstarter price was $199; the retail price has not yet been announced. Like Silicon Dust's other devices, this is a networked tuner; you watch by using an app on your computer, phone, over-the-top box, or smart TV.
I have ordered a Quatro 4K. I will review it when I receive it or when ATSC 3.0 test broadcasts begin in Boston, whichever comes later.
I expect many more tuners to become available in 2021.
