Ok, first, what inspection? Do you mean that if those lights don't work you won't get a license plate? I must say, that's pretty wild. I bet there's lot's of yard service trailers without running lights being towed by teenage boys this summer.
But really, here's your answer....Keep in mind I don't have your year or coach length, but ours are similiar and hopefully equivalent. Since ALL of the fronts are out, and you're SURE that your lights and their grounds are good then it's a single wire problem...somewhere.
Under the front of your coach should be a removable panel in the belly, not far from where the A frame has entered the skin, probably on the curbside. It should be held on with screws. Remove it. Inside you hopefully will find a spaghetti mess of wires. You are looking for GREEN
wires. Green is for the running lights. Find the bigger one that comes from the A frame, it should be coming out of a bigger cable, that's your pigtail. Follow it to a wire nut and there is where the wires to your running lights split off.
I think you should have two smaller wire splitting off at this point, one for the rear and one for the front. First test: Look for a loose small green wire, that would be your problem. Connect it into the bigger green wire coming from the car and see if this solves your problem. If there are two or more small green wires already connected to the big wire, disconnect one and see what lights turn off. If none do, then that was your front wire. See if you can find damage to that wire where it rubs against the frame or touches something else. A mouse may have chewed it.
If none of this works, you will need to
A)determine that all of the lights up top are still wired together. Use a continuity tester and pull ALL of the bulbs off, then go from light to light testing continuity between the lights. If this isn't the case then you have more wiring issues. Solving this gets complicated, so let's leave it for now. OR, you could run a 12 volt
source to one of the hot leads on one of the marker lights, when you have the cover off. They should all light up. Run a jumper wire from your green wire in the panel and see if they light up.
B)Run a new hot wire from the lights down to the big green wire in the belly.
I have guesses on how to run this wire, but don't know from experience how it is really done, so I'll tell you how I saw someone else did it on mine. It looks like they took the green wire down the wall on the inside, maybe they used fishtape through the hole for the wire for the marker light. Then they cut a small hole with a hole saw in the wall inside one of the dinette benches and pulled that wire out. They then drilled down thru the floor and into the belly and connected it back to the green wire. They made a cover for the hole in the wall, BTW. Luckily yours is the front marker lights. The rear would be a pain.
Maybe someone else has a better way, but that should work. BUT make sure you have A) above done first though.