Have you seen the book Manx Slave Traders by Frances Wilkins, published 1999 by Wyre Forest Press, Kidderminster DY10 3NQ (UK), ISBN 1 897725 13 2?

It is full of lists, names, dates, facsimile reproductions of letters and maps. Includes vessels engaged in the Guinea trade, dates, a list of all known Manx captains of vessels operating out of Liverpool and a chronology of key events from 1700 to 1829.

Well worth getting hold of! Good luck.