There are four Prayer Beads you can obtain in the Ashina Outskirts area.
Defeat General Naomori Kawarada
Past the Outskirts Wall - Gate Path sculptor's idol, you'll find General Naomori Kawarada. Defeat him to get a Gourd Seed, along with a Prayer Bead. (Refer to the General Naomori Kawarada's dedicated page for the strategy and video)
Defeat Chained Ogre
You'll encounter this mini-boss past the Outskirts Wall - Stairway sculptor's idol. Defeat it to obtain this Prayer Bead. (Refer to the Chained Ogre's dedicated page for the strategy and video)
Defeat General Tenzen Yamauchi
You'll find this mini-boss after the fortress gate behind the Stairway where you fought the Chained Ogre. (Refer to the General Tenzen Yamauchi's dedicated page for the strategy and video)
Ashina Castle Gate Fortress Secret Chest
After defeating Gyoubu Oniwa, you can access the castle by taking the previously accessible stairs.
You'll encounter the Tengu of Ashina inside. After talking to him (part of a sidequest that will unlock the Ashina Arts skill tree) and opening the other door from the inside, go upstairs and make your way to the broken ceiling.
Use your Grappling Hook to reach the highest wooden beam near the broken ceiling. Walk around the corner then to the middle beam so you can access the opening, jump and hang so you can pull yourself up.
There's only one chest in the attic so open it to get the Prayer Bead. You can watch the video below if you want more details.
How to find the Prayer Bead in Ashina Castle Gate Fortress