Surface water runoff issue ...

I have a large concrete slab leading to a steep garden bed. During heavy rains the surface water runs into this garden bed causing erosion.

To stop this, I want to install a drainage channel at the end of the slab and drain it away properly. The only solution I have seen so far are the ubiquitous EasyDRAIN stormwater channels from Everard - they are too ugly for this purpose and not easy to attach to an existing slab.

All I need is a simple u-shaped channel made of galvanised steel or a plastic similar to the Everard channels. I need about 15 meters so custom designs are out of the question.

Does anyone know of a company or retailer with a decent selection of such u-shaped channels? PS: Bunnings has nothing.

Thanks
Chris