I'm in the US so I don't know how much help this will be for you but I purchased some Browning gear rack and matching pinions from a local engineering supply. The cost was about one-quarter that I found from a photographic dealer. The big source in the US is Boston Gear and perhaps they distribute overseas as well.

As far as darkslide material you might try garolite or some thin aluminum sheet (both sold by McMaster-Carr in the states). I am building a wetplate holder and using garolite. For the light trap, I think some spring aluminum used to attach weatherstripping to screen doors will work once covered with black felt or fine woolen material. The spring aluminum was found at a local hardware store.

Another type of material recommended to me for the light trap was something called "fingerstock" which is a thin metal spring material with fingers cut into it to evenly apply pressure against the opposing wall of the trap. Hinged pieces of hardwood backed by springs or dowels have also been used.

The best souce for the lightrap spring is probably a used modern 4x5 holder. You can cut it down for quarter-plate.