You can still order PSUs directly from Bitmain. Also, when someone cancels or fails to pay for an order they don't tend to publicize a new batch, but rather they add available units to the 'All Products' page that can be directly added to your cart and purchased from there. I'd recommend checking the 'All Products' page frequently (especially the days following sold out batches) as I've ordered many units while the D3 page showed it as being sold out. They had November units available for sale at $1,450 all week before finally selling out yesterday... Not sure how many people are aware of this, so spread the word.
https://shop.bitmain.com/main.htm?lang=en