I think its highly unlikely. (And I don't think its very hard to find US box fins either. Most brands produce US box versions of wave and crossover fins).
The smaller Kombats are really wave/freestyle/crossover boards and when you go between different fin setups you do want to change the position quite a lot (wave forwards, B&J/straightline blasting back). I agree there are limits to how much a US box can take, but for that kind of power sailing you would be better off on a small Futura. Qldsalty, what kind of fins did you break. G10 like the original Drake Crossovers? I would think such a fin would hold up very well, at least of to 30cm size.