No idea where you or I can get them, but for low-tier enterprise archival storage, vendors either put them into their own archival-tier arrays, or buy directly from the HDD vendors.
I think of SMR like Optane. A bunch of consumer-level tech guys w/o a real job got all lit up and started arguing about it online, but its target market was not the "NewEgg website" market, it was the "million dollar storage array from IBM" market.
Remember, there are many workloads that are "write this on disk and keep it forever" - even historical data in a data warehouse showing soda sales by season.
I honestly haven't bought any storage or compute in 25 years - my personal crap is old "enterprise/business line" junk from work.
Where you, as a consumer, can get them - don't. I don't think they're meant to be used by consumers. You're gonna have a bad time unless you write software specific to this weird type of drive. What you might find out there is some kind of a storage 'consumer NAS in a box' product that has tiered storage inside, with these drives and other ones. But stay away from drives on their own w/o that special software in front.