In actuality most 6x9s have similar output characteristics.
What sets them apart is the electrical information sent to them. I speak of a crossover. If the rest of the system is sonically pleasing to you, put a low pass filter set at what ever crossover point you feel meets your need between the amp and the 6x9s.
In the meantime here is a link to a company I use for building speakers for large venues and as it happens for the missile.
http://www.parts-express.com//index.cfm?.
Andrew