That feature was removed at least several months ago, there was a short period in which they gave everyone a chance to download all of their mp3's before it was removed altogether.

Pretty sure there's no way to get them anymore.
From August 26, 2014:

To all fellow UGers,

It's been more than 5 years since we implemented mp3 upload and
store functionality to the website. Unfortunately this feature
never got popular and kept rarely used for all these years.

It's takes server resources and storage space to host all these
files, besides many situations when copyrighted materials were
posted and caused damage to Ultimate Guitar.

After all these years, we decided to remove this functionality.
We are closing UG Mp3 project this coming Monday, September 1th.

You can download your files stored on the website at this page.

UG Team

And yes, the link has long since stopped working. Sorry mate.
Quote by ElMaco
My last pay check was £0 working 0 hours. I can't believe how easy it was
The link to download music was open for many months.
My God, it's full of stars!