You could try Mainport Forwarding in the Netherlands. They are recommended for Sea shipments, but I believe also do air transport.
Also, Motorcycle Express is very experienced in air freight of motorcycles from Europe to North America.
Contact details for both are at:
If you are shipping by air, you may not need to use an agent. Just check with the air cargo division (NOT the regular passenger sales or the Head Office) of the airlines which fly between the two countries you are considering. For example, Lufthansa Air Cargo from Germany to anywhere they fly.
Good luck and let us know how you make out!
"It matters not what goal you seek
Its secret here reposes:
You've got to dig from week to week
To get Results or Roses."
'One world, two wheels'