You can download code practice files from, for example, http://www.arrl.org/code-practice-files. The following is how to make your own practice files.
First, you need to find some text files. I always visit Project Gutenberg, which offers over 42,000 free ebooks in various format including HTML, EPUB, Kindle, and plain text. You will download a book in a plain text format.
% tr -s '[:punct:]' ' ' <original.txt >withoutpunct.txt
You may wish to delete all the punctuations from the text.
% ebook2cw -w 40 -f 600 -s 8000 -b 64 -q 1 -o ChristmasCarol-40wpm ChristmasCarol.txt % ls ChristmasCarol-25wpm0000.mp3 ChristmasCarol-30wpm0000.mp3 ChristmasCarol-35wpm0000.mp3 ChristmasCarol-40wpm0000.mp3
ebook2cw is a program to convert ebooks to Morse MP3s/OGGs files. It might be convenient if you add the options -a and -t to add ID3 tags to the file. Or you can import the files into, say, iTunes, and add the tags there.