It’s old enough now that not many people or even normal wholesalers put them up for sale randomly.
I can recommend this ebay seller who we’ve all shopped with a ton, shipping is slow but free
Despite this, the 42mm bands are still compatible with 44mm, 45mm, and 49mm watches, as stated by Apple. Fit for 42MM/44MM/45MM/49MM Apple watch. Apple watch SE(2022). The smooth, dense material drapes elegantly across your wrist and feels comfortable next to your skin.
www.ebay.com
Also though, trying to find this particular band which is just named “blue” presents a search term issue haha