Once you have level 3 shops set up in your favorite settlement, and a good sized population, it might be time to go out looking to recruit these special level 4 merchants to run the shops.
There are a total of 8 special merchants that you can recruit for your settlements, shown below. These first three can be easily found just by going to their location and speaking with them. You will have to pass a persuasion check in order to recruit them, so I would suggest a quick save before you talk to them, and then just reload if you fail.
Ann Hargraves — Clothing Specialist
Appropriate Assignment: Clothing Emporium
Population Demand: N/A
You can find Ann Hargraves in the WRVR Broadcast Station.
Vault-Tec Rep.
Appropriate Assignment: Trading Emporium
Population Demand: N/A
Found in Goodneighbor at the Rexford Hotel
Holt Combes
Appropriate Assignment: Trading Emporium
Population Demand: N/A
Found in Vault 81 at the depot. Not actually recruitable (cut feature).
For these other five, you'll need to encounter them during your travels in a random encounter, which can be much harder to do and is mainly luck based. They will require a persuasion check in order to be recruited, but you'll also need to have a large enough population to convince them to join you as well.
The Scribe — Armor Specialist
Appropriate Assignment: Armor Emporium
Population Demand: 10
You meet The Scribe during Random Encounter: Workshop Armor Vendor.
Doc Anderson — Clinic Specialist
Appropriate Assignment: Surgery Center
Population Demand: 20
You meet Doc Anderson during Random Encounter: The Walking Wounded.
Ron Staples — Food & Drink Specialist
Appropriate Assignment: Restaurant
Population Demand: 20
You meet Ron Staples during Random Encounter: Time to Party.
Rylee
Appropriate Assignment: Trading Emporium
Population Demand: N/A
You meet during Rylee Random Encounter: Rylee the Trader.
You can also find her after a quest ends in the Longneck Lukowski's Cannery
Smiling Larry — Weapons Specialist
Appropriate Assignment: Weapons Emporium
Population Demand: 30
Randomly encountered at any road in the Commonwealth.
Once you have successfully recruited one of these guys, they'll set up in your shop in your settlement and they'll be selling all sorts of new things, including unique and rare items quite often. Definitely worth the trouble of hunting down the random encounters!
There are a total of 8 special merchants that you can recruit for your settlements, shown below. These first three can be easily found just by going to their location and speaking with them. You will have to pass a persuasion check in order to recruit them, so I would suggest a quick save before you talk to them, and then just reload if you fail.
Ann Hargraves — Clothing Specialist
Appropriate Assignment: Clothing Emporium
Population Demand: N/A
You can find Ann Hargraves in the WRVR Broadcast Station.
Vault-Tec Rep.
Appropriate Assignment: Trading Emporium
Population Demand: N/A
Found in Goodneighbor at the Rexford Hotel
Holt Combes
Appropriate Assignment: Trading Emporium
Population Demand: N/A
Found in Vault 81 at the depot. Not actually recruitable (cut feature).
For these other five, you'll need to encounter them during your travels in a random encounter, which can be much harder to do and is mainly luck based. They will require a persuasion check in order to be recruited, but you'll also need to have a large enough population to convince them to join you as well.
The Scribe — Armor Specialist
Appropriate Assignment: Armor Emporium
Population Demand: 10
You meet The Scribe during Random Encounter: Workshop Armor Vendor.
Doc Anderson — Clinic Specialist
Appropriate Assignment: Surgery Center
Population Demand: 20
You meet Doc Anderson during Random Encounter: The Walking Wounded.
Ron Staples — Food & Drink Specialist
Appropriate Assignment: Restaurant
Population Demand: 20
You meet Ron Staples during Random Encounter: Time to Party.
Rylee
Appropriate Assignment: Trading Emporium
Population Demand: N/A
You meet during Rylee Random Encounter: Rylee the Trader.
You can also find her after a quest ends in the Longneck Lukowski's Cannery
Smiling Larry — Weapons Specialist
Appropriate Assignment: Weapons Emporium
Population Demand: 30
Randomly encountered at any road in the Commonwealth.
Once you have successfully recruited one of these guys, they'll set up in your shop in your settlement and they'll be selling all sorts of new things, including unique and rare items quite often. Definitely worth the trouble of hunting down the random encounters!