You can probably find the cable on eBay or buy one from RT Systems (
RT Systems Radio Programming Software). The Yaesu FT-50 cable will do the job.
Search around on the web for the program. It's a DOS program. You'll need a computer that runs DOS or that you can boot into DOS. Running the program from a DOS box in Windows won't work.
Because you will be running in DOS, don't plan on using a USB port on the computer. You'll probably need a real serial port.