I get a lot of them from boliviamall.com and alpacamall.com; these are good sources if you’re interested in getting a quena (my personal favorite) and want to help support makers/sellers where the flute actually comes from.
If you’re interested in easy to learn (but not as much room to grow), you might like a Native American flute. Douglas Thunderhorse makes great flutes that can be purchased online through weed path music shop.com, or wind dancer flutes (Roger McGee) can also be found by web search.
If you’re particular to the Irish flute, honestly I’ve seen a lot of good deals on flutes of all kinds on eBay. Irish flute is one I haven’t had the chance to try yet, but I imagine it’s similar in many ways to the Quena.