If I can't find an appropriate existing piece of furniture, I often group several boxes to approximate an item. Boxes can be resized to make panels, legs, and other components. The boxes can be coloured or textured as appropriate.

Boxes can also be grouped with existing furniture items. This can be combined with hiding parts of existing items where they have a unique material, just set the material to invisible.

I sometimes google for models I can import.

Finally, I sometimes use the open source 3D modeler ArtOfIllusion and build a model, but that's hard work.