have a look at http://www.ee.surrey.ac.uk/Contrib/manx/history/tynwald/tynwald.htm
celebrates with a Norse style open air parliament Midsummers day (or eve)
Christianised into St John's feast day

re National saint - there aint one tho St Patrick might just about sneak in (tho St Germa(i)n, or Maccul (Maughold etc) run him second)