Acquiring an accent can take quite a long time, so firstly don't worry excessively. It is a good idea to record yourself. When you play your recordings, how analytical are you? You say your accent isn't very convincing, but are you trying to identify the particular areas that are causing this? If you can identify sounds, stress, etc, that cause trouble, they can be worked on. Have you used a mirror? If you look into a mirror when you're speaking, it can make it easier to get your mouth into the right position.
There are some other sites here where you will find listening materials:
Listening - ESL Web Directory - UsingEnglish.com
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