Mike we have used an expansion chassis from these guys, http://www.magma.com/ they may have what you're looking for.
From: Mike Dini [mailto:firstname.lastname@example.org]
Sent: Thursday, November 07, 2002 7:05 PM
Subject: Connecting PCI Expansion card cages together
Who makes products that allow for expanding PCI systems by connecting PCI
card cages together?