I remember when Port Adelaide joined the comp in 1997, how Geelong's John Barnes became a trivia question - he kicked a goal in their Round 3 match to become the first player to score a goal against 17 clubs. (Counting Brisbane Bears and Brisbane Lions as one club.) He'd scored a goal against Geelong when playing for Essendon in 1987-90.
This afternoon I was wondering... who was the first to kick a goal against 18 clubs? Turns out it's... Barry Hall.
Hall's third senior game for St Kilda in 1996 was against Fitzroy, he kicked one goal. In 2011 he played for Western Bulldogs against Gold Coast, and bagged 5 majors. (No need to worry about Brisbane Bears here: he never played against them.)
Nobody yet has scored against 19 or more clubs. Brent Harvey debuted in 1996 but he never played against Fitzroy, plus he was a one-club player. Dustin Fletcher played against everyone (except Essendon) but never scored a goal against GC or GWS. Shaun Burgoyne didn't debut until 2002 so he's only scored against the current 18. So it looks like nobody will, unless new teams come in...