AFAIK, there's no way to predict when an item that's out of stock on Tesla's Web store will come back in stock. The best you can do is to click the link to be notified by e-mail and then watch your in-box carefully. These adapters tend to stay in stock for very short periods, and AFAIK there's no way to reserve one, so it's a mad rush when they come back in stock.
There are a couple of alternatives. One is to buy on eBay or from some other online store. Some of these listings are basically scalpers, but some are non-sleazy owners who've decided to sell their used devices. Either way, though, prices are likely to be high. Also, be sure you get a
US-spec model. The last I checked, I saw a lot of European CHAdeMO adapters on eBay, and those won't work in the US, because the Tesla-side plug won't fit.
The second alternative is the
Setec CCS adapter. This is a third-party device, so there's some risk of it failing in the future because of a Tesla software update; and some people are not comfortable using a third-party adapter. It's also more expensive than Tesla's CHAdeMO adapter, at $563.99 from its official US distributor,
Lectron. There's a
very long thread on it
here. Be aware that early posts in that thread are heavy on problems, but most of those were resolved with device firmware updates. The device is still not 100% reliable, but it's much better than it was in December, when it was introduced in the US. CCS might or might not be more common than CHAdeMO in your area; you'll have to check PlugShare or other apps to find local stations.