Great question — answering as the UphillTech team:
If you're working in certain countries there is http://www.7digital.com/affiliates Also, there is eMusic which is a little different as it's a subscription: http://www.emusic.com/affiliate/partner.html
Full answer by Joe Simpson: https://stackoverflow.stackexchange.com/a/4773765 (CC BY-SA 4.0).
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