Once you get out of Europe the Isuzu brand becomes more common, they have a lot of badge engineering deals with local companies, so often you will see an Isuzu lookalike with (eg; in Australia) a Holden badge and another name - Jackaroo. I'd expect that Australia has more aftermarket items for the Troopers than most countries - have a look at ARB - they maybe able to help with special orders into the UK for things like winch bars, full length roof racks, storage systems.
Parts support is fair, but like anything Japanese thats not a current model parts tend to get rare and expensive.
The Trooper is not a hardcore offroad vehicle, its a muddy road 4x4, often called a "softroader". The front ends were/are notorious for being soft and running out of toe in adjustment if driven on "bad" (corrugated, potholed) roads.
You need to do some serious research about bringing any vehicle into Australia as its not as easy as driving across to France. There are plenty of threads on the Australia New Zealand forum about private imports/carnets etc.