You use a broker. That takes care of any export license (if one is needed). But still, rather expensive. Shipping and probably quarantine. Not to mention that the type of birds good enough to import aren't going to be cheap to purchase.
Coming into the USA, the quarantine is what gets you.
It might be worth it for top quality of something not locally available. One would assume there would be a market for chicks after you received your birds so there is the possibility to recoups some of the expense.
I've sent many dogs to and from Britain, and it costs, but the procedure isn't difficult. You just have to be organized and do everything right on schedule and have the right paperwork.
I've got my eye on some Pomeranian geese from Norway, but the cost of quarantine is stopping me.