There isn't enough information to adequately work with here. When you say that the woofer needs to be replaced, which of the following really applies?
1. The foam surround is rotted-out but the rest of the woofer is still OK.
2. The foam surround is rotted-out and the speaker has been driven/bumped in that condition resulting in a trashed voice coil.
3. The voice coil is shot yet the surround is intact.
If item 1 is your scenario, by all means, repair the woofer. You can do it yourself but I've seen older messages that referred to certain audio repair shops that specialized in this work. The messages are located either at the Audio Asylum or Audiogon websites.
If the voice-coil is shot, I don't know if there is a suitable replacement woofer available.
Mr. Kidknow