It says in his profile that he has a 73 J4000. Welcome to the club. In 73, the interior and beds were updated. You should be able to get a turn signal switch from any parts store; same steering column as GMs. As for the front lens covers; I take it you're talking about the running lights/turn signal covers. As 73 was a crossover year, there can be an early 73 lens that had a 2-piece cover with a clear over amber lens or a 1- piece with an amber lens alone. I have seen both on 73s and the 1-piece can be substituted for the older style 2-piece.
As for parts availability, post in the wanted forum for your lenses (they were used on Cheros and Wags too) and there is a tailgate on Ebay right now. The tailgates are a little difficult to come by but any J truck from 73-87 wil have the gate you need. I also restored a 73 and do have some parts I've gathered over the years if you're looking for anything else.
73 J4000 "The $LUT" 360 V8 bored .040 over Edelbrock 2131 1407 4V carb K8600 cam Dual Flowmaster 40 mufflers TH400 QT 3.73 Dana 44s
78 Cherokee Chief WT "Old Blue" 360 V8 4V TH400 QT
05 Jeep Grand Cherokee 3.7 V6 5 speed automatic with new QT