Inge has stair runner meshes for her stairs/maxis staircases @
Simlogical. They are the same meshes Mabra is using and should be really quick to recolor, but I don't think any are designed for modular stairs.
However, if the mod stairs are running between two floors, I would think they'd be the same height/shape as a staircase so you *should* be able to use the runner.
Dina, I believe I have some old modular Chic stairs from T$R that have a "runner" on them. I'll check.