According to that document, it cost the Canadian government over a billion dollars just to mitigate a substantial fraction of the risk in one province. It talks

According to that document, it cost the Canadian government over a billion dollars just to mitigate a substantial fraction of the risk in one province. It talks about them installing protection devices to reduce the risk of damage - just reduce, not completely eliminate - on a thousand of the most at-risk transformers. I don't think having the ability to replace 9 transformers is going to help much here. Sure, the failure of the correct combination of 9 might be able to shut down the grid. That's only likely to happen as the result of a direct, human-planned attack - any disaster would inevitably have to destroy more than the minimum to get a correct combination, probably including a whole bunch of smaller transformers. And crucially, destroying just those key transformers alone wouldn't be enough to stop the grid from being restarted - the generation infrastructure is distributed locally throughout the grid, so even if regions couldn't be reconnected they could operate independently with reduced reliability and capacity if necessary. In order to cause a massive months-long blackout that killed 90% of Americans, any event would have to destroy a whole bunch of local, distributed infrastructure, and stockpiling a handful of transformers would not be enough to replace that.