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
Select a delivery method: for instant arrival or Printable Card to give it in person. Pick a digital card design and complete the purchase.
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
Choose a membership duration or search for a specific title to gift.