Yes F is no longer available on the EZE route....hopefully a change to a 747 will see it back. CW is comfortable enough.
If you can be flexible with your dates then you should be able to get what you want but you'll have to keep looking regularly. What time of year were you thinking of travelling? I would avoid coming between December and March as Buenos Aires is not a very comfortable place to be due to the heat. Outwith these months availability tends to be better as well.