Fts 34.46 Hz
Mms 78.59 g/m/s
Cms 0.2714 mm/N
Rms 2.3037 ns/M
Vas 10.65 ft3
Re 3.39 ohms
Le 0.96 mH
Qms 7.39
Qes 0.410
Qts 0.390
Xmax 8.20mm
BL 11.88
EBP 84.4
eff 2.91%
Sens 96dB
Max Pwr 150rms

The Cornwall cabinet is about 7ft3 and tuned to ~35Hz. So you could do pretty well with an Omega 15 or Magnum 15HO. Either one would be a big step up for not much more money than the stock replacement. As for the midrange and tweeter, you could perhaps find those on eBay. The midrange is a K55 and the tweeter is a K77.

Alternatively, you could make your own midrange and drive it with a small cone driver like the Alpha 6 and crossover to a PSD2002 on an H290 horn flare. Or you might even shoehorn in the midhorn I use, which would span the entire width of the speaker between the woofer and tweeter, and fill in the vertical space between them too. Naturally, either of these options will require some cabinet modifications.