Amazon.com: APC AP940-1525A UPS Communications Smart-UPS Signalling Serial RS-232 Cable DB9 to RJ45 (RJ50) - Same as AP940-1525C and AP940-0625A But a Longer Cable : Electronics
USB to RJ12 6P6C RS232 FTDI Serial Converter APC PDU Cable for APC UPS 940-0144 - Walmart.com
6FT DB9 to RS-232 RJ11 6P6C Serial Cable for APC UPS Compatible with APC Rack PDU AP78xx AP79xx AP86xx AP88xx AP89xx - Walmart.com
KVM-SERIAL Configuration Information and Assistance | APC United Kingdom