Yeah, it is very widely available. Try searching amazon. National Public Radio has done the whole trilogy as well as a bunch of EU. They even have one episode (which is available for free on the net because it is nolonger commercially available) called Mission to Ord Mantell, which takes place between Star Wars and ESB. It also contains a Luke flirting with Leia scene. It is pretty poorly done though, all the characters have to reuse lines from the trilogy. One notable part is where Luke says "Come on Han ol' buddy, don't let me down" which is very annoying because he is using a Lando line that chronologically hasn't even been spoken yet. It is still an interesting episode though, but if you listen to it first don't judge the other NPR productions on its standards, they are far superior. Also the NPR trilogy feature Mark Hamill, Billy D, and Anthony Daniels repraising their roles.

I checked amazon,

here is the adaption of Star Wars on seven CDs:

http://www.amazon.com/Star-Wars-Original-Radio-Drama/dp/1565110056/ref=pd_bbs_2/002-4286046-5276053?ie=UTF8&s=books&qid=1175993052&sr=8-2

And here is the whole trilogy on 15 CDs:

http://www.amazon.com/Complete-Star-Wars-Trilogy-Episodes/dp/1565111648/ref=pd_bbs_1/002-4286046-5276053?ie=UTF8&s=books&qid=1175993284&sr=8-1

I high recommend them, but as you can see, they are pretty expensive. Probably they can be found a lot cheaper on ebay. If you live in the US, I have found that they are very common in Public Libraries, and even if they are not in your local library chances are a nearby library has then and can obtain them through interlibrary loan for you quite quickly. There are 29 Episodes in all, the first 13 of which are all based off the first film, Empire Strikes Back and Return of the Jedi both being considerably shorter.

The Mp3 for mission to Ord Mantell can be downloaded from theforce.net here.
But again, this is considerably lower quality than the others, so don't listen to it and decide not to bother with them. The others are considerably better done.