you could hire a Polish plumber to listen to for a week, but you'd end up sounding like a Polish plumber. In their own country, they just sound like normal, local people; so as others have suggested, your own normal speech should do.
Farrell's accent was carefully calculated. The idea was that an Irish accent would sound to English (or American) ears a bit parochial, not quite mainstream, which is how Macedonian Alexander would have sounded in sophisticated Greek ears.