Way back when, it was legal to just send plants back and forth across the oceans. Now we have to pay fees for different documents and inspections to receive plants from other countries.
Then there was a group in the U.S. that started hybridizing for new varieties. That is how we have so many new varieties in the U.S. over the decades.
There are a few of us that have purchased from Fernwood (England) and Erwin Geiger (Germany), but it is very expensive.