TECHTOO 4 Port Professional FTDI CHIP USB to RS232 Serial Cable DB9 Serial Adapter Converter 9-Pin Male to Male with Hexnuts https://www.amazon.com/dp/B00Z6JQ13A/ref=cm_sw_r_cp_api_i_4PLXCbKP7QHQ9
If you have a need for multiple ports, they do make 4-n-1 adapter cables now.