Hi,
There are no crew agreements prior to about 1860. There are some muster rolls, kept at the National Archives, which vary in the amount of information they provide. They are filed by port and vessel, I believe. The Maritime History Archive in Newfoundland has microfilm of the muster rolls for Plymouth and Dartmouth (1755-1808), not sure what the year range is for other ports.
I guess you've seen the Slade collection at MHA?
J.