A few weeks ago, a few specific Google Play Edition (GPE) devices went out of stock. It wasn’t known if they would be coming back, but now it appears they are fully discontinued.
The devices in question were the 2013 HTC One, the LG G Pad 8.3, and the Sony Z Ultra. All of these devices were released in 2013 and have been replaced with new models. The Samsung Galaxy S4 GPE is still on the store, even though it’s out of stock, but if a GPE Galaxy S5 is released, it will probably disappear as well.
So if you want a Google Play Edition device, your options are now limited to the GPE HTC One (M8) and the GPE Moto G. If you wanted one of the now discontinued devices, you will have to buy one from elsewhere.