Advertisement on smashboards is just posting your major tournament in every regional social thread. You're Armada so you can get away with it, but even lesser known players (such as myself) are able to advertise similarly as long as it isn't over the top and annoying.
Bunbun is right, I hadn't heard about hardly any European tournaments at all except for BEAST II. I think if you guys start branching out and socializing with some of the US crowd then you'll see more US interest. Your problem isn't interest, it's information.
1) Promote Euro tournaments you want to make international (people can't go if they don't know it exists)
2) Provide information so people can see it's not that hard to travel international (flights, prices, discounts, etc.). You can probably arrange with a major flight company to get a nice group deal if you can guarantee 20+ international flights or something. Big businesses got is as successful as they are partly because they're good at recognizing profitable arrangements and then jumping on them. People will go if you show them it's not as difficult/costly as they thought.
It's not as hopeless as you think, I promise :D