Bought all the Pokémon on 7th and didn’t get Corin

[Awhitt523]

So I just got back to reborn after the 13th badge and went to police HQ to continue the stolen Pokémon but it won’t trigger I’m guessing because I don’t remember seeing Corin on 7th street am I SOL on this side quest now?? The DJ already arrested the black market guy on 7th 

[Saslen]

To my understanding, buying all the Pokemon on 7th Street is unrelated to the Corin Rouge quest. That has to do with the Mega-Z quest.

 

The general outline of the Corin Rouge quest is as follows:

1. Buy the Pokemon from the Grand Hall. It gets stolen;
2. Track the thieves to the northern Peridot Ward only to find that some kid already stole it from them;
3. Find that guy in the Obsidia Slums and fight him, only to find that he already sold the Pokemon to some gang member;
4. After joining the gangs, you need to talk to both the Magma Gang member just south of the Nightclub and the Aqua Gang member west of the Lapis Ward Gym. One of them bought it from the slums kid, and the other stole it from the first gang member and sold it on 7th Street;
5. After that, Corin shows up on 7th Street.
6. Next steps. In the interest of not spoiling the questline, I'll leave it at that.

 

I'm guessing that you missed step 4, so Corin never spawned in. I don't know if the gang members' locations change post-Restoration, but since you can apparently find the slums kid from step 3 later, it would be strange if you couldn't complete step 4 post-Restoration.