Go to Contest Hall and talk to this girl with purple hair and purple dress. She is the Gym Leader, Fantina, who has ghost types.
Blackthorne city is not in Pokemon Diamond but in Pokemon Heart Gold/Soul Silver
The first gym in Pokemon diamond is in Oreburgh City
The 7th leader is Candice in Snowpoint City
hearthome city leader
Pastoria City
Pastiora
orebourgh city
eterna city
Heart Home City.
The 6th gym leader is in Canalave City.
The 6th Gym Leader on diamond in Byron. Bryon has Steel Pokemon and is located in Canalave City. Canalave City is to the west of Jubilife City.
In Veilstone City