They don't. Two reasons. First, Alembics come in so many shapes and sizes that they typically stay with the bass for which they are built. Second, I am not sure how long the foam is good for. By the time someone is willing to sell, it may not be so protective. If this is a 30 year old road case, it may need to be redone.
What's it worth? Depends on condition and if you need it. If you don't need it, it isn't worth the cost of shipping and storage. If you do, it could easily be worth $400 or so.