Rokeby -
I've always liked these :
16" Truck/Van '88-91 (#CHV185)
However, I don't know if the wheels on trucks are different from the wheels on cars. What I mean is, I don't know if the hubcaps are interchangeable.
I found them here :
Chevrolet Truck Hubcaps, Chevrolet Truck Wheel Covers and hub caps - Hubcaps.com
CarloSW2