Companies could deploy directory synchronization tools or full metadirectory services that hook up their directories to trading partners' directories. But with hundreds of trading partners in complex e-business relationships, manageability and security issues would ensue. Lightweight Directory Access Protocol referral, which allows you to get information on the fly from another company's directory, seems promising on the surface. But planners have not been comfortable losing the security, availability and performance assurances that come from controlling their directories. They also haven't been entirely comfortable with opening up their directories to external inquiries.
Community directories represent yet another architecture alternative.
Find a industry association or service provider and get them to host a copy of directory information for each organization in a group of like-minded trading partners. Of course, most companies would need to belong to multiple communities. You'll need to combine elements of one or more e-business directory management approaches. Buy or build some technology. And stay flexible.