Are you sure you looked at the "slim" Banana Republic trousers? They will specifically label them "slim" and not just "classic" and "regular." Zara is a good choice, their line is Euro cut and will usually be slimmer.
If you have the money, John Varvatos, Brooks Brothers, Band of Outsiders, Brioni, and Zegna generally makes some good slim fitting ones. Zegna is actually my favorite because they provide fabric to many of the other designers, so they will have a wider assortment of fabrics and patterns. You can also get them to custom make you some pants or a whole suit if you would like.