No, foreign powder is not banned--but there have been some practical problems involved in getting it here.
In the case of Hodgdon's Australian-made powders, in normal times one ship at a time could bring plenty over. When demand spiked one ship wouldn't hold enough powder, so they started sending two ships or more. The trouble occurred in the Auckland, New Zealand seaport, where they stop to refuel. The Kiwis got nervous about having TWO ships full of powder in the harbor at once, so said only one could be there at any given time. This naturally put a crimp in the supply-line.
The reason Ramshot's Belgian-made rifle powders aren't as available (aside from far more demand, that is) is the plant over there had a fire last year. It didn't damage the entire plant, and while the repairs have been made, production was reduced so they could do plenty of safety-testing while bringing everything up to speed. But they are anticipating supplies will be up to NORMAL soon. However, that doesn't mean demand will be down to NORMAL anytime in the near future.
Dunno what's happening with powder from Scandinavia, but do known demand has been outstripping supply there as well.
