Soundcloud doesn’t make it easy to access the MP3 files of your hosted tracks. They are there, but you have to dig a bit deep. This tool will help you locate your MP3s, but only if you are on the podcasting service.
You may find this updated Soundcloud extractor more helpful.
SoundCloud MP3 Extractor
Please note this is very much in beta. Please let me know if you notice any bugs or issues. Full instructions to follow.