6ft (1.8m) DB9 F/F Serial RS232 Null Modem Cable - Black | Serial RS232 | Computer Cables | USB and PC
Building the Null Modem Cable
DB9 Male to Male NULL Modem Gender Changer RS232 to RS232 - PLCCable.com - Automation Supplies and PLC Tools
C2G 50ft Serial RS232 DB9 Null Modem Cable with Low Profile Connectors FF In Wall CMG Rated 50 ft Serial Data Transfer Cable First End 1 x 9 pin DB 9 RS
Null modem - Wikipedia
Crossover or "Null Modem" vs. Straight Through Serial Cable - Decisive Tactics, Inc.
RS232 null modem | Null modem adapter
What is the schematic of an RS232 Null-Modem? - Ferguson Wiki