if you still have the old woofer, have it rebuilt. There are a number of shops that will do it. Short of finding a cherry one cheap on ebay, you may not do better $-wise anywhere.
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From my personal observations owning those speakers, it is hightly probably that the surround of all woofers are beginning to disintegrate and one of them has disintegrated more than the others, but all surrounds should be looked into and most likely need replacement. Even the one that buzzes might still be repairable by merely replacing the surrounds. You can most likely make a judgement upon removing the covers and observing the operations of each speaker one by one.
Try Allisonacoustics.com for the factory replacements. I think that they might be close to the originals-I don't know. I know that Roy Allison is associated (once again) with the company somehow. I have a pair of Allison Seven's that had rotten surrounds and I ended up finding a pair of more modern AL 115's from which I took out the woofers and the tweeters. They sound great now. Allison had new drivers for them and I was all ready to fork out a bunch of money but ran across the Al 115's. I have done new surrounds on other speakers and they work pretty well but I'd prefer new drivers if you can find them. Good luck!