Hey man, I just thought of a couple of resources for you to check into:
1.
http://www.partschannel.com/. I have had excellent luck with them and parts for my 82 Toyota. You either have to find a local store (can buy direct at their store) or have to go through a local parts store who deals with them, really worth checking into.
2. More obvious and pricey, but try your local isuza dealer's parts department, I have a loyalty card with my local toyota dealer, paid about $50 and get 10% all parts and labor (they do no labor to the truck), but I have gotten a few parts from them.
3.Keep in mind its a hit and miss, they may or may not carry it, but I think its worth looking into.
Good luck.