To acquire the Calus Mini-Tool in Destiny 2, you should focus on activities and sources relevant to its drop cycle. Initially introduced during the Season of Opulence, this submachine gun often becomes available through various in-game activities that rotate with each season.
Check the rewards for current seasonal activities or specific events that might feature legacy weapons. The Calus Mini-Tool could be included in loot tables for these activities, making it obtainable by participating and completing these events.
Additionally, keep an eye on the Gunsmith's inventory or potential drops from Umbral Engrams if the weapon is part of the loot pool in the current or upcoming seasons. Decrypting Umbral Engrams and focusing them towards specific weapon loot can increase your chances of getting the Calus Mini-Tool. Stay updated with the game's patch notes and community updates for any changes to weapon drop sources.