Mr. Wills
Information on the gross domestic product and the population sizes of the Crown Dependencies is publicly available on their respective Government websites:
Jersey (it should be noted that Jersey measures gross value added, not gross domestic product):
http://www.gov.je/ChiefMinister/International+Relations/Profile+of+Jersey.htm
Guernsey:
http://www.gov.gg/ccm/navigation/about-guernsey/economy/
Isle of Man:
http://www.gov.im/treasury/economic/data/income.xml