Something like this: https://www.amazon.com/BQKOZFIN-Compact-Waterproof-Durable-Carrying/dp/B09CD177M8/ref=sr_1_1_sspa?crid=15V1CM2L01NWS&keywords=cajon+bag&qid=1645519853&sprefix=cajon+%2Caps%2C174&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzNDZHRVY0RzE5Q1hYJmVuY3J5cHRlZElkPUEwNDA2MDA4TTBZTDBIU1NPMzNDJmVuY3J5cHRlZEFkSWQ9QTAxOTE1MTkySDFWT0I0N0gyTkNEJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==
There are many models for different prices, just check if they have the correct dimension.
You can find them also in music stores of course.