I want to become better at attacking my opponent's king when they castle queenside. What are some grandmaster games where the player who castles queenside gets mated or loses due to a powerful attack on the queenside?
That's a pretty typical scenario, you'll find a lot of examples if you search for games in the sicilian opening.
[Event "Sarajevo"] [Site "Sarajevo BIH"] [Date "2000.05.29"] [EventDate "2000.05.17"] [Round "11"] [Result "0-1"] [White "Sergei Movsesian"] [Black "Garry Kasparov"] [ECO "B90"] [WhiteElo "?"] [BlackElo "?"] [PlyCount "64"] [fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"] 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Be3 e6 7.f3 b5 8.Qd2 Nbd7 9.O-O-O Bb7 10.g4 Nb6 11.Qf2 Nfd7 12.Kb1 Rc8 13.Bd3 Rxc3 14.bxc3 Qc7 15.Ne2 Be7 16.g5 O-O 17.h4 Na4 18.Bc1 Ne5 19.h5 d5 20.Qh2 Bd6 21.Qh3 Nxd3 22.cxd3 b4 23.cxb4 Rc8 24.Ka1 dxe4 25.fxe4 Bxe4 26.g6 Bxh1 27.Qxh1 Bxb4 28.gxf7+ Kf8 29.Qg2 Rb8 30.Bb2 Nxb2 31.Nd4 Nxd1 32.Nxe6+ Kxf7 0-1