Can You Buy "Commentaries" Of DVDs Without The Shows

I bought a used copy of the Simpsons season 4 and I do enjoy listening to the commentaries on the DVDs. But truthfully I have seen all the Simpsons so many times now, I don’t need the DVDs. We get the Simpsons, three times a day, five days a week in Chicago anyway.

Is there anyway to buy the commentaries only. I don’t really need to look at the DVDs as it is with these DVDs I was working on my computer and just listening to them anyway.

The only example I have seen is for Dr Horrible, for which the commentary track were also songs, and released separately as a CD.

The official BBC Doctor Who site has episode commentaries available for free listening, but they’re region-blocked. So unless you’re a British Whovian, I got nothin’.