This batch file will "moveto player" the 4 random encounter level 4 merchants (Smiling Larry, Doc Anderson, Ron Staples and The Scribe) 

while in the settlement you want these merchants to trade open up the console and type "bat merchants" 

this will spawn the 4 NPCs next to you then all you need to do is open the settlement interface, move them to the settlement you want them in and then you can assign them to the tier 3 stores you've built.

I've not included the other 4 as they're stationary and easy to find and recruit (and one of them needs a quest to be completed)