I think you should sit down and listen to an old guy - me - for a minute here.
Fact #1 - Isuzus were orphans when they were new. They don't even make them any more.
Fact #2 - Aftermarket parts is/are a BIG business.
Fact #3 - Isuzus needing aftermarket parts, although it's something YOU might want - is not a great big market.
Fact #4 - Your requests, needs or desires hold little sway with people who manufacture performance parts for more popular vehicles.
Fact #5 - Aftermarket companies view Isuzu owners like the crazy aunt you keep in the attic when company comes to visit.
Fact # 6 - Chances of finding some high performance parts at the age of our vehicles is possible on two levels:
Wishful thinking possibility #1 - There's always someone with something they made or are harboring from days of yore that you might need or want - but they too are becoming few and far between. EXTINCT is a better word.
Wishful thinking possibility #2 - The person in #1 will not sell you anything they have unless it's an estate sale and the wife wants to get rid of 'all that junk for the first $20.00'. You will arrive at the sale and the guy who just bought it all is driving out the driveway as you drive in - and he's taking it to the recyclers.
Wishful thinking possibility #3 - On the day it rains soup, you'll only have a fork.
Wishful thinking possibility #4 - There is NO wishful thinking possibility #4.