Question: pokemon ultra sun and moon where to get more beast balls?
Answer: Receive 3 from Lusamine at the Altar of Sunne/Moone after defeating Ultra Necrozma.
Receive 5 from Dulse/Soliera at Poni Grove to catch Blacephalon/Stakataka.
Buy at Aether Paradise reception, one for 1000 Poké Dollars and 10 for 10.000 Poké Dollars.