Where do you get lombre in Pokemon SoulSilver?

Yeah, you can find Lombre in Sapphire and Ruby as well as in Emerald..

But it's either you find Lombre, in the Sea or Near the water's edge, no specific place. Or you find Lotad and make him evolve instead.

Lotad is in the place where Wally caught his Ralts (But as I catch Pokemon there, II never saw a Ralts) . In case you don't know where that place is, it's in Route 102, a little bit to the right of Petalburg, and you can find Poochyena, Wurmple, Zigzagoon and Seedot there, too.

Just in case you don't find it there, try looking a bit further South or East.

And just to tell you, if you don't want your Lombre to evolve, make him hold an

Everstone (You can find it in Granite Cave, Dewford Town). But if you do, use a Leaf Stone. (You can trade it for something in a place near Mossdeep City.)