That just doesn't make sense. The Slav is a variation of the Queen's Gambit. If you were to use the same moves against something else it wouldn't be a Slav and wouldn't be called one. It wouldn't even give a similar type of game, since in the Slav it's crucial that Black has the option of playing ...dxc4 at various moments. Without a pawn there, it's not a Slav.
Against things like the London, you need to pick some variation of the London, and so on for other tries for White after 1.d4 d5.
Luckily, amongst people who know opening theory (the people you want to use opening theory against), the queen's gambit is easily the most popular option for white.
I was looking for a book which discusses the use of the slav against any 1 d4 opening (not just the queen's gambit). For that matter, use of the slav against anything other than 1 e4.
I don't see anything out there, except not sure about Silmans book 'The Slav versus 1 d4' - anyone know if that has coverage other than QG?
For that matter, do you think just studying the slav against the QG is enough to prepare someone for using it against any 1 d4 opening?