There are several towed 4.2in Mortars in private hands in Aust. John Belfield's museum has one, Cowra has one, the Gold Coast musuem has one (For sale!), and there are one or two in private collections. All highly sought after for their 8.25-10 tyres for fitment to a 6pdr AT gun!
These were in Aust Army reserve stocks intil the mid 80's.
The 4.2in Mortar pictured at the top of this thread is a rarer version, but the one pictured is from the Bandiana museum.