How can I make Emil show up at the Resistance Camp?

Technically, there is not a way to make Emil drive by the Resistance Camp; it's random where he spawns, but that route is definitely less common than the one in front of the Desert Zone. All you can do is make him respawn and hope he shows up on the route that takes him by the Resistance Camp. I personally reloaded the area repeatedly until he was in the right place, but according to this video I found, you can make him respawn without reloading the area, which vastly reduces the amount of time you will spend trying to get him to show up by the Resistance Camp.

The video says to do this in Chapter 7-1.

The steps laid out in the video are:

• Finish the Forest Kingdom chapter
• Talk to Emil at least once
• Run (don't fast travel) to the abandoned commercial facility
• Run about halfway across the bridge back to the City Ruins and check on Emil's location.
• Run back into the abandoned commercial facility if he is not on the correct route.

Repeat the last two steps until he shows up.

It's worth mentioning that you need to shoot Emil at the right time for him to land in front of the Resistance Camp, as there have been numerous reports of Emil not selling the good stuff even though he was driving along the correct route. The proper timing of this is also included in that video around the 3:10 mark.