I have a friend who has recently gone blind.
Try bard.loc.gov
The files won't be in mp3 format, but rather DAISY format.
If they don't have it, then probably the only legal option is to purchase the CDs/mp3 from CBD. Other Christian, or even secular bookstores might have them, but since more than one person I know has gone broke saving money by purchasing their Christian material from CBD ....
FWIW, my favorite audio Bible is Inspired By .... The Bible Experience. The voice actors are African Americans, such as Denzel Washington, Blaire Underwood, Ertha Kitt, Monique, Natalie Cole, Angela Bassett, etc.
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It might be easier to obtain a gratis copy of the NIV in Braille, than in mp3 format.
jonathon