I'm 99% sure that Von Schweikert doesn't have replacement bass drivers. I don't know who the original manufacturer was, but Albert Von Schweikert had them apply a coating to the cone of the drivers. I'm not sure if it added stiffness, or what.
I don't know if they still do it, but Von Schweikert did have a program where you could send your VR-4s to them and they would replace all of the drivers and crossovers as a big upgrade. It wasn't cheap, so I opted to go with new speakers instead and pass my VR-4s down to my kids.
Matt at VS is very helpful. I've also had phone conversations with Damon Von Schweikert and Leif Swanson. Very nice people.

