Hi there. I have a 1999 trooper and use Raj, at Williams Hunt spares in Randburg, JHB. Ph:011 438 0600. I have found that certain spares have to be ordered from Japan, and you have to pay up-front. I have replaced an electric aerial, headlight and gear shift; many of the spares are held in PE main warehouse.
Hope that helps. There is also an Isuzu forum, which is managed by an Isuzu Trooper guy. Perhaps he can give some advice.
1999 Isuzu Trooper - The Truck
2002 Landcruiser 105 - The Grey Nomad