Your friend has a legal gun shop in Greece and is not already selling American firearms?
Or does he want to cut out the middlemen importers/distributors and do direct importation for resale?
First one is so common as to make me wonder what else about the situation you describe is hinkey. Since I am not aware of any large firearms manufacturing industry in Greece I imagine his current stock is coming from other countries. Why stuff from the USA would be any different escapes me.
Second one is going to make a lot of people unhappy, for he will be cutting folks out of the chain of baksheesh. It can be done, though. And the paperwork on the American side is probably the easiest part of the process.
Be sure to let him know that ATF has a special price if he can guarantee the guns will go to narcotraffickers, of which Greece has its fair share.:uhoh: Given the economic conditions in Greece I am willing to guess his biggest problem will be trying to buy on credit from anybody.
stay safe.