Flash Catalyst is meant to be that..
it is however - imho - quite hard to use it in a practical environment where there is a workflow like
design > dev > design update > dev > design update > dev
since Flash Catalyst really only works one way.
It's a good attempt from adobe but it's not quite there yet.
You can use it however to do the design slicing yourself, export the result to a separate project and import into your current flex project.
Get a trial and see for yourself.
I don't know of any other "tool". You can export your graphics from the design document and import them as assets manually otherwise.. but that gets tedious quickly..
I'd be interested to know if anyone has a better solution..