What happens when the other country isn't willing to sell? Consider a war or other disaster e.g. in the months before the pandemic, China stopped the export of face masks and other PPE, resulting in shortages in hospitals around the world.
PPE shortages in hospitals were because of unprecedented demand levels, not because China didn't continue to export it. A country is actually a lot more likely to have problems handling that kind of short term demand shock if it relies entirely on domestic manufacturing
If not - the politics is involved in selling decision making - then the US starts a sanctions war, as China example shows. It sells in the end, but after being economically punished.