Some of the quests in World of Warcraft: Shadowlands aren’t as specific as others, and this includes Rare Resources. The brokers ask you to find three Coins of Brokerage for this quest, and to get them, you’re required to find the coins “anywhere in the Shadowlands.” We’ll narrow this down a bit for you.
The easiest location to find all three coins you need will be in Bastion. Specifically, you’re looking for the Beasts of Bastion rare location at 55.2, 80.6. Once you arrive, speak to Orator Kloe, and summon all four of the beasts. You may not get the coins to drop from the beasts each time, but you can keep asking Kloe to bring them back. This will give you all the coins you need in a matter of minutes, rather than hunting all over the entire expansion for another location.
If you decide to go elsewhere, keep your eyes out for rare enemies and treasures that appear on your minimap. Occasionally, you might get an enemy to drop more than one Coin of Brokerage; the Faeflayers in the northeast portions of Ardenweald tend to be generous with their drops. Rare Resources is a great quest to stack on top of aiming for the achievement tasks involved with the Treasures world quests in each zone.