The 2500 serial ports use a 60 pin connector....the cable is called a DB-60 to DB-60 back to back cable. You can order some cheap at many websites. One such would be www.anthonypanda.com. YOu might even get some of them cheap at ebay.
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus