One can assume that, if the AirTags are now in production, you might be able to buy them soon. Keep in mind Nikkei has a great track at revealing Apple-related news, especially when it comes to leaks coming from Cupertino's supply chain. Also, the AirTags have extensively leaked over the past year, with most reports claiming they are due imminently and will be able to attach to clothing or other things to help you wirelessly locate items.
AirTags are supposed to work with Apple’s Find My app and should resemble small circular discs. Perhaps their most exciting feature is that they're rumoured to offer offline finding, meaning they may not require a Wi-Fi or cellular connection to be located. They're thought to feature ultra-wideband radio technology, similar to the U1 chip in the iPhone 11, in order to process offline capabilities. We have an entire rumour roundup on AirTags here.
As for when these little trackers will appear, a recent Bloomberg report claimed AirTags are still in development and could come with a leather carrying case. However, Bloomberg’s Mark Gurman also said they could be part of Apple’s autumn product launch. Apple has announced an event for 15 September, but Gurman believes this event is for new iPad Pros and new Apple Watches. A separate event for the iPhone might happen in October.
It's unclear which event we'll see the AirTags debut at, but if Nikkei's report is legit, they will likely launch this autumn either way.