Audible does not sell physical, "pre-paid" gift cards in stores. Instead, you can purchase Audible Gift Memberships or specific audiobooks as gifts directly through their website. Gift Membership Options
Since Amazon owns Audible, you can sometimes use an Amazon Gift Card to pay for Audible content, but there are restrictions: Gift an audiobook - Audible Help buy audible gift card
💡 : If you gift a membership to someone who already has an Audible account, they will receive all the credits from the gift at once without interrupting their current billing cycle. Using Amazon Gift Cards Audible does not sell physical, "pre-paid" gift cards