I have an imported diesel Isuzu and as has been said the American counterpart is a source for nearly all parts except my engine and rhd associated mechanics. (Edit: also the transmission but that's not necessarily true for every import)
If you're handy just do the work yourself unless you have a trusted mechanic willing to do a lot of "that'll have to do" stuff. Even though there's often parts available from us counterpart vehicles keep in mind imports have to be over 25 years old so there are certain things that can be a pain to find .
Fortunately, a lot of these vehicles are still in operation in the UK, nz, au, and random Asian countries and you can have some luck shopping around and having stuff shipped.