I guess it depends on where you live and what resources are available to you, but here in Portland I figure out what I need for spindle length, and I take the original spindle and a cheap-o digital caliper ($8 @ Harbor Freight) down to a few shops that have collections of new and used spindles. I find one in the right length using the caliper and compare shoulders to find a close match. Usually I can find a good match. Recently I had some trouble finding one long enough to fit Sugino cups with TA cranks on my Raleigh, but usually it's not a problem. If you get Campy cups and a spindle you can try that method. Hope that helps

Cheers,
Karl