8 speed cassettes are available on Ebay. Miche has also made Campy-compatible 8-speed cassettes. Then there are 8-speed Ergopower shifters, which are also available on Ebay, but they may need rebuilding.

I have a couple of bikes with 8-speed Ergopower shifters, and they are as ergonomic, precise and smooth as my newer 10 and 11-speed mechanical units. Campagnolo got Ergopower right almost from the start.