Tripp Lite 18in USB to Null Modem Serial Adapter FTDI w/ COM Retention M/F 18" - serial adapter - USB - RS-232 - U209-18N-NULL - USB Adapters - CDW.com
4g Usb Modem Fdd Tdd | Mbps 3g Usb Modem | F 4g Usb Modem | Modem Router | 4g Dongel - 4g Usb - Aliexpress
3ft DB9 F/F Null Modem Cable
StarTech.com 2m Black DB9 RS232 Serial Null Modem Cable F/F - DB9 Female to Female - 9 pin RS232 Null Modem Cable - 2 meter, Black - Walmart.com