Amazon has opened pre-orders for Avatar: The Last Airbender The Complete Series 15th Anniversary SteelBook Collection. According to the product page, the Blu-Ray bundle will be coming out on Feb. 18, 2020, in the U.S. region. If you are interested, you can pre-order with the following link from the online retailer:
You can also check out the steelbook design with the image placed just below this paragraph.
So, if you are a fan of the television series, then you might want to check out the 15th Anniversary SteelBook Collection.