Hello Paul
Like you I've been let down by the blanks on old-maps site. However I have a couple of 'Godfrey' maps of West Bromwich. The1885 (North) West Brom one has a small area of Black Lake on it, mostly around the colliery and GWR railway area. If you think it may be of use I'll try and scan it and send it to you.
Jeanette