Oireachtas na Gaeilge is on in Letterkenny the last weekend of Oct, so there is bound to be music there. Especially good event to be at if you like seán nós singing, in Irish & unaccompanied.

Farless convenient to Milford, the Shamrock at Falcarragh, Sat nights I believe. I know the Mon night sessions at Gaoth Dobhair, mentioned by Peter K (Fionn) are still going strong