To expand on what Paul says, two lots each of 20 brake vans were built for the MoS in 1941/2. They were a modified version of the SR 25T van, the most noticeable difference being the two vacuum cylinders mounted on the end platform. 24 vans remained in the UK and 16 were sent to the Middle East and Persia. One van was seen at Quishon, Israel, in 1988 and may be preserved.
Of the UK vans, many were modified in some manner by the army over the years and at least 10 went to preserved lines. Two were sold to BR (LMR) in 1949 and were numbered M360327 and M360328. One still exists at Longmoor Camp with a couple of other army wagons as part of FIBUA (Fighting In Built Up Areas) training ground. However, neither the wagons nor the track they stand on have any connection with the original Longmoor Military Railway.
It is probably a vain hope but it would be nice if someone could produce a conversion kit to produce an MoS van from the Bachmann model.
Finally, here is an example I photographed at Longmoor in August 1964.
Tony