There is now another aftermarket spring manufacturer who is making springs for the Mirage. H&R now has a drop spring kit that lowers the car approximately 30mm. The part number is 28831-1 for anyone wanting to see if they can get them.
Francismd has already installed these on his Mirage and says:
Spring rate is outstanding. The car wallowing is significantly reduced compared to the stock springs when driving on uneven road. I can tell this has significantly improved because previously on the stock springs, the light cut-off from my projector headlamps would seem to bounce up and down when running on uneven road (I am not sure if this is noticeable for the stock halogen HLs). I now have minimal movement in my light cutoff using the H&R springs. I don't have any problems with the current absorber. I just find the stock springs too soft = jerky steering wheel on high speed and bumps, body roll on cornering. I now have better handling in spirited highway drives, and no more rolling during cornering and high speed curves/turns.
I am currently checking for availability in the US. I'm guessing if they aren't available now, they will be shortly. I'll update this thread more as there is more info available.