The flies that are linked on this pater are word pairs that exchange ‘r’ and ‘l’ sounds. They are organized into separate files per word pair and the name of the file is the word pair.
Download the files (more keep coming) and put them on your phone, ipod, or other device you used to listen to music. Listen to them randomly and see if you can identify the word pairs. Practice saying the back. Many devices give you the ability to slow the audio down, so you should try that to help you make the sounds.
There is a PDF file at the end of this page that is the list of words.