Lyndn Baines Johnson (LBJ) was the 36th President of the United States and served from 1963-1969. So all legislation that he signed would be during that period. Wikipedia has a list of all the legislation from 1901-2001 here. The list is not complete, but contains all of the most significant legislation.
You'll be looking for the years when he was President, so '63 through '69, so the 88th, 89th, and 90th Congresses. You'll need to do some additional research to see which legislation from the 91st Congress were signed by LBJ.