When I've looked for confirmation that LBJ said the first quote when signing the Civil Rights act, I haven't found anything solid. It matches many other confirmed comments and actions from him, so it would not be the least bit surprising. Just curious if you or anyone else reading has a good source for that quote.
It was attributed to LBJ in several books, so there is no internet link with the handy quote.
However, the leftist bedwetters at Snopes declared that this quote has been debunked and therefore false, so pretty much every story one can find claims it is a false quote.
If you can find it attributed in multiple actual physical books, that fact tends to lend far more credibility than the internet.
Sorry, that isn't a ton of help. But you know how lefties control the web and information.