https://www.jetpens.com/Lihit-Lab-Altna-Carrying-Sleeve-Small-Gray/pd/24824<br /> Lihit Lab Altna Carrying Sleeve - Small - Gray<br /> $30.50

B6 is 4.9 x 6.9 inches, so just slightly larger than 4 x 6 inches

https://www.jetpens.com/Lihit-Lab-Smart-Fit-Carrying-Pouch-A6-Olive/pd/12378

Lihit Lab Smart Fit Carrying Pouch - A6 - Olive<br /> $21.50