6' Null Modem 9 Pin (DB9) Serial Male - Female Cable
Amazon.com: StarTech.com 2m Black DB9 RS232 Serial Null Modem Cable F/M - DB9 Male to Female - 9 pin Null Modem Cable - 1x DB9 (M), 1x DB9 (F), Black (SCNM9FM2MBK) : Electronics
StarTech.com USB to Serial Adapter - Null Modem - FTDI USB UART Chip - DB9 ( 9-pin) - USB to RS232 Adapter - Add a Null Modem RS232 serial port to your laptop
Null modem - Wikipedia
Kentek 6 Feet FT DB9 Female to DB25 Male Null Modem Serial Printer Cable Adapter Cord 28 AWG F/M Molded D-SUB RS-232 Crossover 9 to 25 Pin for PC Mac Serial Device -