With all things come change, iTunes is no longer working with Linkshare the affiliate partner that allowed commissions. However you can work directly with iTunes, see below:
As a valuable member of the iTunes, App Store, iBook Store and Mac App Store affiliate program, we want to alert you to some important program changes. We are no longer using the Linkshare or DGM networks, so if you are an affiliate in these programs, you need to migrate to the new program.
We have improved and expanded our program to create a more global platform with enhanced reporting capabilities. The new program will pay 7% commission on eligible sales within a 24-hour purchase window. You can use the same new affiliate tracking token for US, Canada, Mexico, Australia, New Zealand, Russia, Japan and more. Tradedoubler links are not effected by this change.
Performance Horizon Group (PHG) will support our new affiliate program. To continue earning commissions without interruption, you must set up a new affiliate account on the PHG network and update all existing Linkshare and DGM affiliate links before October 1st, 2013.
Signing up for the new program is easy. We will review and approve your application quickly. Once approved, you will receive a welcome email with more information on how to create new PHG affiliate links.
If you have any questions, please review the FAQ on the affiliate resource site at http://www.apple.com/itunes/affiliates/resources/ or contact us on our affiliate help desk at http://affiliate.itunes.apple.com/support
The iTunes Affiliate Team
iTunes, App Store, iBookstore, and Mac App Store Affiliate Program