In normal use breaking chains it is very rare to break a pin, however if you do require a spare pin they are available for sale here
Price: $9.50 ea plus $1.00 postage
Ball bearing chain riveting part.
The small grub screw that stops the chain pin pushing out the rear of the chainbreaker now has a ball bearing pressed in, this makes flaring rivet links much easier and more effective, it also greatly minimises the chance of breaking the tools pin when using this way.
Price: $12.50 plus $1.00 postage