Veilstone City
You should go to Canalave city
Cobble badge
Beat the gym leader
Snowpoint City.
The mine badge.
it is Mauville gym
In Diamond, Pearl and Platinum 7th gym is in Snowpoint Town.
By beating the gym leader
the fourth gym is in celadon city at the bottom left of the city. the gym leader is erika. the badge is called the rainbow badge
== == You get the 8th gym badge in Sunyshore City. Hope this helps
Go to hearthome city and beat the gym.
After you get the Cobble badge from the Veilstone gym.