Zeeb is correct is most reguards. We ship overseas but the cost of shipping is much more expensive. Most shipping companies only allow 3 day air for international shipments which can get expensive. Although we ship international our customers pay the exact shipping cost (same as they do in the U.S). I think you will find this with most U.S. companies.
I have never had a problem with customs. At most the plane is held just a day or so. Also, there aren't any duty charges for a single plane. In most count cases there aren't duty charges with large orders of planes. You can also get the planes insured. It just becomes more of a problem if the plane is damaged because the shipping is so expensive. To replace parts or the plane shipping is what will get you.
If you want to find a company that will ship to Ireland the best way is to call or email the company that you are interested in. Most U.S. companies will work with you as long as you pay shipping.