Hi Lee,
Had the opposite problem, needed another 3 kgs to balance all my gear, someone suggested dumbbell wieghts which I tried. They are cheap but boy are they hard to drill out! and you can`t lock them in position also.
Got a wieght made up at the local engineers, 35mm hole and a grub screw to hold in place for a total of $26. Made from a offcut of mild steel bar 90mm round and about 100mm long I picked up. Good coat of paint and looks like a bought one.
That would be the easiest way to go for you....
Cheers Gary