A series of bibliographies by Clifford, Greene, and Vance covers most of the scholarship on Johnson in the last century: James Clifford and Donald J. Greene, Samuel Johnson: A Survey and Bibliography of Critical Studies (Minneapolis: Univ. of Minnesota Press, 1970) will get you through 1969 or so (it's in fact a combination of two earlier volumes), and Donald J. Greene and John A. Vance, A Bibliography of Johnsonian Studies, 1970-1985 (Victoria: Univ. of Victoria, 1987) goes much of the rest of the way. I've added my own modest efforts, in an on-line bibliography covering 1986 to the present.
A more specialized bibliography: Samuel Johnson's Library: An Annotated Guide, ed. Donald J. Greene (Victoria: English Literary Studies, 1975), is a guide to the books in Johnson's library.
This is part of a Guide to Samuel Johnson by Jack Lynch. Comments are welcome.