Anywhere. All plans are found everywhere. They are drops like any other item. Good luck.
That said, you acquire them pretty quickly with regular play. For myself for example, playing probably 5/7 days out of the week (more than most I'd certainly wager), over the past three weeks since making my first foray into RoS Hardcore, I've gotten almost every single level 70 plan there is. Only missing Griswold's, Fleeting Strap, Umbral Oath and Utar's Roar. I've primarily found them in rifts (Torment 1 and up) but definitely gotten a couple while doing bounties.
All of the plans are world drops, they can drop anywhere, any mob, any difficulty. So there's not really any advice we can give you on where to look for them.
I wonder where to find "Hallowed protectors" plan to teach the blacksmith?
Another question please. Is there any place that i can read about where to find all the plans for the blacksmith.
Thanks for your help
That said, you acquire them pretty quickly with regular play. For myself for example, playing probably 5/7 days out of the week (more than most I'd certainly wager), over the past three weeks since making my first foray into RoS Hardcore, I've gotten almost every single level 70 plan there is. Only missing Griswold's, Fleeting Strap, Umbral Oath and Utar's Roar. I've primarily found them in rifts (Torment 1 and up) but definitely gotten a couple while doing bounties.