The Summoning Rock
The Summoning Rock is classified as a collectible type of item. Despite its classification, it has a resale value of one meso. High-level users, especially priests, employ the Summoning Rock to summon creatures to aid them while in battle. You need 30 Summoning Rocks for the Huckle's Spirit Pouch quest.
Alcaster's Shop
Alcaster is an elderly wizard located in the El Nath Market. He runs a shop that sells a variety of magical items, including the Summoning Rock. However, his shop becomes available only after you complete the In Search of the Book of Ancient quest and the Alcaster and the Dark Crystal quest for him. You need a Level 60 character to complete both quests. After you complete both quests, you can purchase the Summoning Rock from Alcaster's shop for 5,000 mesos. Although it is a hefty price, it may be worth the time it saves if you need only one Summoning Rock.
Erasing the Trace
Erasing the Trace is a Level 87 quest in Edelstein, which is a continent you can access through a portal in the center of Victoria Island. Once in Edelstein, speak to Allen at the Gellimer Research Lab. He will tell you that the lab is overrun with Security System monsters. Defeat 300 Security System monsters in the lab and return to Allen. He will give you 10 Summoning Rocks.
Monsters
A variety of monsters drop the Summoning Rock. However, it is a relatively rare drop for most monsters, and you may have to kill them repeatedly to receive the amount you desire. The Summoning Rock is dropped by magical and undead creatures such as the Dead Scarecrow, Skelegon and King Goblin. The best place to grind for Summoning Rocks is in the Haunted House. The Rotting Skeletons within the Haunted House frequently drop Summoning Rocks.