Check out the Mavic Ksyrium Race or Ksyrium Elite ... both come in well under $500.
Not sure why you're hung up on flat (bladed) spokes ?? ...bladed typically means heavier and the aero advantages don't come easy. At this price point you'll have a tough time finding a thin, light AND bladed spoke wheelset.

Those two Mavic sets are work horses. They're not heavy by any means (for the <$500 range) and they hold up well. I have an old set of Elites that I bought to keep in the SAG and I ride them occasionally in training. ...And you can buy Mavic stuff just about anywhere. I never had a warranty claim, but I can't imagine that a company like Neuvation has the same dealer support that Mavic does. Hub bodies are also easy to swap out if you ever go from Shimano to Campy (just FYI)