I am looking to find out some games in pgn/cbh format played by GM's against substantially below rated players(say 1200-2000).The only games I found out is some 20 games played in ICC charity simul by anand few years ago.Is there any collection of games of simul/exibition/casual to have?
I'm sure there's a book out with that title. Also The Amatuer's Mind by Jeremy Silman has games with an IM v amatuers.
There's a book with that very title an it's exactly what you're looking for.
It starts out with 1200 players and moves up to IM I think.
If you have Chessbase you can construct a filter. When the filter screen comes up, select the rating range for the amateurs - say, 1600-2000 ELO for "One" player- and nothing else, just click "OK". Then filter those results by setting the range at 2200-2800 for "One" again, and it should give you all the games with one master and one amateur.
The Euwe & Kramer book Chess Master vs Chess Amateur is very good at illustrating the typical mistakes in thinking strong amateurs make. They were one of the best writing teams in chess.