I was wondering how you got on with your dissertation?
Did you manage to find any primary source material ?

The reference below was used to support an entry o wikapaedia ( yeah i know these are suspect some times but it may be worth investigation)

"The number of convicts transported to North America is not verified although it has been estimated to be 50,000 by Dr John Dunmore Lang. These went originally to New England, the majority of prisoners taken in battle from Ireland and Scotland. Some were sold as slaves to the Southern states.[4]

[4]^ Bound for America. The Transportation of British Convicts to the Colonies, 1718-1775 by A. Roger Ekirch.