I've been considering something similar to contain the ballast on my 'soon to be built' line. Both on suspended sections / bridge bases but also set into the top of embankments. All with weed control material to stop the ballast running through the holes. i was looking for some wide enough to carry twin tracks and found these people.
Direct channel do cable tray upto 600mm wide.
Medium Duty Premier Range
Available Sizes - 50mm, 75mm, 100mm, 150mm, 225mm, 300mm, 450mm & 600mm Widths x 3 Meter lengths
With a 25mm Return Flange
Pre-Galvanised.
See link below.
Medium Duty Premier Range
Regards,
Paul.
NB: They also carry zinc galvanising spray and brush on paint in a range of colours.