Send Jerry Lemond a note for the headlights themselves.
He can get you new Isuzu parts cheaper than anywhere else.
He may also have some good used ones that he'll see ya.

As far as protecting them, try using 3M rock guard.
It's a heavy MIL clear plastic film that is used
to protect the paint.
Isuzu used the stuff on the rear doors on some of the vehicles
where the wiper rested on the door.
They also used it on the lower rock guards on the Troopers.

You should be able to get it at any auto paint supply house.
It's a little pricey, but it works well.

1995 Trooper LS auto 3.2 DOHC /w SOHC intake
1989 Trooper 2.6 auto
1989 I-Mark RS DOHC 1.6
1991 Stylus XS DOHC 1.8