As far as I know, access to uranium is tightly controlled for obvious reasons, but hydrogen is everywhere, and even getting access to deuterium shouldn’t be too hard.
There is also the fact that most modern thermonuclear bombs “only” use the fission bomb to trigger the hydrogen bomb.
People demonstrate achieving fusion all the time. The problem is getting useful energy out of it. When building a bomb, we don’t really care about useful energy; we just want to release a lot of it.
So why aren’t people building purely fusion based thermonuclear weapons left and right?
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While the fusion of Hydrogen into Helium releases more energy than it needs to start, fusion still requires a LOT of energy to even start. So much that it only naturally occurs in stars and supernovae. So for a fusion bomb to work, there has to be another massive burst of energy to get the fusion reaction going.
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