If you want to practice transcription, you can download podcasts, interviews, etc., off of the internet. Unfortunately, most of these do not include transcripts and may not be true examples of what you will encounter while working as these are more controlled and have much clearer audio.

You can locate audio and transcripts online by searching for: transcript audio. A lot of the results (only looking at the first two or three pages) seem to be political in nature. Among others, this search brought up the Norman Finkelstein & Former Israeli Foreign Minister Shlomo Ben-Ami Debate: Complete Transcript at http://www.democracynow.org/finkelstein-benami.shtml. If you explore this site you will find that there are also plenty of other transcripts.

Another result this search brought up is American Public Media linked to a public radio program, "Speaking of Faith with Krista Tippett" http://speakingoffaith.publicradio.org/programs/index.shtml. You can download podcasts and the free transcripts are available for online viewing. Click on the program you are interested in transcribing, download it, and when you want to check your finished work against the transcript, you can access the transcript under Program Details on your left-hand side and click Transcript.

You may also want to try search variations of various media types, such as transcript mp3. This search seems to give you a bit more variety (earnings calls, as well as political and government (http://www.fda.gov/bbs/transcripts/), etc.

Although I have not checked the results, you may also want to try other variations, such as transcript wav, or transcript wma. I'm sure there are other searches you can do that will bring up results, but this will get you started.

While I haven't checked the site and audio, the user Chitchat at Workplace Like Home posted www.stenospeed.com that also has practice audio and some text.