Gary,
I don't think you will ever find a 1.5 ton M-H cart, but check out
www.fergietrailershop.co.uk where you will see they are reproducing the Ferguson 1.5 ton cart, dig deep in your pocket and a completed unit would look great behind your Gray Pony. Originals are very hard to find of the 1.5 ton, far more of the 3 ton models around.
Malcolm.
www.fergietrailershop.co.uk