I imagine you guys have found the Library of Congress’s National Jukebox already – I search on “Irish” and turned up a bunch of stuff from the early 1900s, lots of which is our of copyright and hence you can listen online:
http://www.loc.gov/jukebox/search/results?q=irish
They have a ton of stuff from all genres. I’ve done so many searches on their Italian genre music as well, and the jazz stuff is a treasure house as well. You guys have probably already heard all of this, though.