Export from flash as flv; that should import to CS5 Premiere as long as you pay attention to the codec options here:
Then do just as you describe to export audio only for you flash project.
Along with Stanley's suggestion, I would like to add - use PCM/WAV, instead of MP3. First, you will have better Audio, and second, MP3 files can be problematic.
Also, Audition has the capability to display Video, and allow one to work heavily on Audio. Do not recall the Video format limitations in Audition, so one might need to do an "intermediate" Video file, in say DV-AVI format, but this is only the "reference file," so any degrading in quality will be moot, as one would not use it for anything else, but the Audio editing, while viewing it.
PS - Audition might be able to handle the FLV, but I just do not know for sure.
Guys thanks for the input, all of it helps. I was able to import an swf and had no problems with importing the mp3. Since I come from a music engineering background I just need to learn how to edit the audio with PR . Once I did the rest was easy, I would normally in the past used Cubase which is a pro audio recording program which lets you import .movs so I would have done it that way but the only way to do was to convert the Flash.swf to an .mov but the presentation is 25 minutes, took forever so I had to look for another solution and got the job done with PR.
Very glad that all worked for you.
Though I do not know it, it appears that Cubase probably has issues, such as I suspect with Audition. The choice of DAW is up to what the user has available.
PrPro has pretty good Audio-editing capabilities already, and when it falls short, I just reach for Audition (have not really put the newer versions of SoundBooth to a test, so cannot comment on any limitations there), even if I do an Export for a reference file for the Video. Keeping things in one program has many benefits, and usually saves a lot of time and effort.
Now, if SmartSound would just do their Sonicfire Pro 5 to work within PrPro CS5, like they did with FCP! That would save me a lot of reference Video file Exports, when scoring. They claim that it's in the works, but I have not seen anything new, on that front, for quite awhile.
Good luck, and thanks for reporting your success!
PS - one of the biggest issues with MP3 source material, is when there are other "things" inside the MP3's, like album art, etc. Nice that yours worked fine.