Sometimes, these parameters will return blank string. You can use the Windows API function GetProfileString() to retrieve the associated driver and port from the Windows.ini file. Example:

uses Printers;
{$IFNDEF WIN32}
 const MAX_PATH =  44;
{$ENDIF}
procedure TForm .Button Click(Sender: TObject);
var
  pDevice : pChar;
  pDriver : pChar;
  pPort   : pChar;
  hDMode : THandle;
begin
  if PrintDialog .Execute then begin
    GetMem(pDevice, cchDeviceName);
    GetMem(pDriver, MAX_PATH);
    GetMem(pPort, MAX_PATH);
    Printer.GetPrinter(pDevice, pDriver, pPort, hDMode);
    if lStrLen(pDriver) = 0 then begin
      GetProfileString('Devices', pDevice, '', pDriver, MAX_PATH);
      pDriver[pos(',', pDriver) -  ] := #0;
    end;
    if lStrLen(pPort) = 0 then begin
      GetProfileString('Devices', pDevice, '', pPort, MAX_PATH);
      lStrCpy(pPort,  @pPort[lStrLen(pPort)+2]);
    end;
    Memo .Lines.Add('Device := ' + StrPas(pDevice));
    Memo .Lines.Add('Driver := ' + StrPas(pDriver));
    Memo .Lines.Add('Port := ' + StrPas(pPort));
    FreeMem(pDevice, cchDeviceName);
    FreeMem(pDriver, MAX_PATH);
    FreeMem(pPort, MAX_PATH);
  end;
end;