Hope you can work it out with the seller, though it sounds like they have skipped town. If you end up trying to repair these, keep an eye on eBay. I see random NOS parts (drivers, crossovers, brackets, etc.) listed frequently. Also it appears that VA shared some components between the Bach, Mozart, Waltz, Beethoven, and possibly other models from that era (Theatro, Maestro, maybe even Haydn?) So you might find some suitable parts donor speakers for cheap. But they did have small changes throughout the years as they went from the original designs to the "Concert Grand" and "SE"/"Symphony Edition" so you'll have to verify compatibility somehow.
There are also licensed distributors that can obtain repair parts from Vienna. I went through Bluebird to get some VA parts a few years ago.