I can't help with Kintyre or Cowal, but when I was on Arran earlier this year there were four sessions a week there. I went to one at Kildonan and one at Whiting Bay, on Monday and Thursday I think it was. At Kildonan the session was led by two people using amplification (but not too much). They encouraged me to join in from the floor with my concertina, and stopped from time to time for other floor singers. My wife, who is not very "folky", really enjoyed it. The Whiting Bay session was more conventional.
See www.arranfolkclub.co.uk