Amazon has Kensizer 20-Pack Fruit Fly Trap (https://amzn.to/3V4H1qP), Yellow Sticky Gnat Traps Killer for Indoor/Outdoor Flying Plant Insect Like Fungus Gnats, Whiteflies, Aphids, Leaf Miners - 6x8 in, Twist Ties Included, for $6.64
Shipping is free with Prime or order over $35.