Bradbury’s stories appeared in a 1950s radio show called Dimension X Radio Drama. For some reason these radio plays are not covered by copyright and are in the public domain. Since they are derivative works, I somehow doubt this. On the other hand, the audio from these radio dramas are so wide spread and available free from so many sources that they have entered the public domain.
Here are some Bradbury stories. Listen to these on your computer or download them to your iPod or iPhone and listen on your way to work.