We received an email from Richard Armstrong with this link to a YouTube video of the last railcar at Foxton:
"Further information for you is that the last passenger train on the Foxton Branch was on Saturday 18th July 1959 hauled by steam locomotive A 601 a YouTube clip of this trip can be seen here: Foxton Last Train 18 July 1959.avi
The last freight train ran a few days after and the line formally closed on the 27th July 1959."