Celestion makes good (great if You're a guitarist
) speakers, but You'll probably find better and broader selection for bass instrument from Eminence for example.
From the Eminence website You can also look at the recommended enclosures for different applications and see if the dimensions match Your cabinet.
That leaves the -pleasurable to some, PITA to some- designing and tuning process out of the equation.
Based on the experience I have about 10" & 12" bass combo enclosures vs. the drivers in them, I'd guess that finding a replacement will be a bit difficult.
The enclosures are generally on the small side.