i'm pretty sure they dont have kits but i know you can take soft parts from different subs and motors from others and make a custom sub but i wouldn't try it unless you have experience i know my homie Hunter has done this a few times atleast i think.
well the soft parts can be bought to build or rebuild a woofer. unls=ess you want to build your own motor. lol that takes some resources. but as far as soft parts you can buy recones or individual pieces. just takes exp and patience