The wagons in Danny's photo above are Ospreys, which are Salmons converted to carry 60 ft track panels without the need for so much strapping down, by the addition of robust stanchions at each end and in the middle. Mick (New Bryford) noted recently that some Ospreys are now being converted back to Salmon.
Cambrian make an excellent kit of the Salmon, which can be converted to Osprey with 3D printed parts.
Flangeway make a RTR Salmon, which has had some length issues in 1st batch, now resolved, although the modern versions of the wagon are not yet available.