I don't understand your problem. You said you thought you would use the GetFTP processor to pull files. This should work fine for you. The processor allows you to specify the port (default to 21) for FTP.
If you want to connect to a server via FTP, then the server has to expose the FTP service. If the server doesn't have FTP enabled and you are not able to enable it for one reason or another, you could configure Apache httpd or nginx web servers to serve up the files and perhaps use the GetHTTP processor.
Another option would be to install NiFi on the server in question and use NiFi Site-to-Site to transfer the files from one NiFi instance to another.