It is online at http://www.manxnotebook.com/fulltext/hist1900/index.htm
(or at least that dealing with 1266 onwards - before this date Moore was obviously unaware of recent research.
This + another 100+ Manx monographs are on my website - a CD ROM of which cost 15 dollars without need for currency conversion - reprints of Moore readily available via any Manx Bookshop - see my website under Organsations etc for address inc email - the Manx Museum will ship on credit card orders