I saw some pixel pro 7 volume buttons on AliExpress website. They're really cheap or inexpensive I should say. I had the volume button fall off on mine and it's so frustrating! I also read a review that mentioned the little tiny rubber piece that goes with it which is good to know. I'm hoping it's still stuck in the phone. I'm hesitant to order from any third party vendor but I don't know how long I can go without a volume button. Thanks to Google for the design flaw on an $900 phone. Frigging ridiculous. Here are a couple more places to try:DHGate and SaleHoo Goodluck!
