Re Athlone/Leitrim:

Sean's Bar in Athlone used to have good sessions - but is now mostly heavily amplified for tourists, as far as I know. Worth asking the staff there about options along the river.

Similarly, Glasson, just outside Athlone, and The Pigeons (I kid you not), a mile or two further out, also had weekly sessions. Both excellent pubs even without music!

Regards

p.s. Some fourteen years ago, Josephine and I were married - with celebrations in and around Glasson! On the day after the ceremony, we and our guests started a session in Grogan's Pub, in the village, at 2 p.m. The music and singing continued till 2 o'clock the following morning, non-stop. At that stage, the pub/restaurant manager appeared with trays of glasses and half a dozen bottles of champagne! "Now, will ye go home?" sez she, grinning!