No third party Vitalsource extension exists for Magento.
Build custom Vitalsource extension to allow customers to purchase e-books via Magento and redeem their publications via Vitalsource (for three-way access to books: online, downloaded and mobile).
Customer Experience: customer purchases e-book from Magento store. Email order confirmation contains a link to instructions on how to redeem e-book. Order confirmation also contains a Vitalsource bookshelf code (for each item). Customer order history contain bookshelf codes for all items and also redemption links/instructions. To redeem an e-book, customers will visit Vitalsource .com directly, create an account or login to existing account, and enter bookshelf code (to redeem book).