You can call Klipsch and get genuine Klipsch parts.  They will request pictures of the badges on the back of your Khorns.  Once you provide that they will be able to provide you the proper parts.

Or you could identify which woofer you have and put a WTB in the garage sale section.  If you go with a different version many folks would recommend you buy two.

Northwest Speaker in Smyrna can fix the woofer. 

Your project sounds exciting! Have you any updates already?  As for the suggestions, here are some of mine:  Double studding is a great idea as it creates a break in the path of the sound waves, which can significantly reduce sound transmission. Use specialized sound-damping insulation like Rockwool or fiberglass to absorb sound and prevent it from traveling through the walls and floors. Insulating between the first and second floors can also help. Consider adding MLV between the studs or under the drywall. It’s a dense material that can help block sound. For the walls and ceilings, using resilient channels or sound isolation clips to decouple the drywall from the framing can prevent sound vibrations from traveling through the structure. Instal acoustic panels. It'll help absorb sound and reduce echo, making the room sound better and preventing sound from escaping. Adding carpets or rugs to the floor can also absorb sound and reduce noise transmission through the floor. Ensure that the doors and windows in the room are well-sealed, using weatherstripping or door sweeps to close any gaps where sound might escape. As for your concern about sound-damping insulation hurting the bass, it’s generally more about the room’s acoustics than the insulation affecting the bass directly. Proper placement of your Klipschorns and room treatment with bass traps in the corners can help manage bass response within the room. I think this all should be able to significantly reduce sound transmission. 

Is anything being done to deliver a quasi-linear phase response?  if so, is that being done via PEQ or via FIR filters?  I think the world is in for a treat when these are released, active crossovers and 2" mid drivers are game changers. 

LOL!  If Hovland was still around, I'd use nothing else. 

Mike that is actually very cool  And in our lingo very hip 🤘😎

Used to be 1-800-Klipsch would get you to the parts department.    I thought Crites woofers were cheaper than OEM Klipsch.  If Crites woofers meet K-33-E specs, they will work in your Khorns.    You should be able to get the bad one reconed at a local pro audio shop.