I purchased 3/8" rubber grommets at the hardware store.
I purchased the airlocks at a local wine and beer hobby store. They have all kinds of groovy stuff!
DIY Airlocks https://traditionalcookingschool.com/food-preparation/kitchen-tools/diy-airlock-fruit-and-veggie-ferments/?utm_campaign=autoblog&utm_source=blog&utm_medium=bloglink&utm_content=DIY+Airlock%3A+Fruit+and+Veggie+Ferments