Hi Petkula73,
I have just, by strange coincidence, been looking for almost exactly the same redemption (from LHR) over the past few days - in summary I think we are both stuck until ~May when TAM (JJ) will release their award seats (they do so 6 months in advance), personally I need 2 seats and haven't managed to find those and my dates are slightly more flexible.
The best I could find was 2 LH seats in C to GRU (Sao Paulo) around this time, and then to add on an internal TAM flight 3 months before the flight. My own view from Air Canada is that they only ever seem to release 1 C seat (not sure why) - looking at all the LHR-YYZ flights in December most have only a single seat available, not quite sure why. The return flight was going to be a challenge!
However I'd be curious if you do get any useful suggestions I can reuse myself
Edit: Oh, and there may be some TK flights from IST-GRU again which you could get availability on and then later on add the internal JJ flights in 3/6months (Not sure whether a GRU-EZE flight counts under the 3 or 6 month rule) - in general, lots of availability to GRU (Sao Paulo) and not much to EZE