Where are the other 8 gyms in Pokemon silver?

You're right! I apologize for the mistake. There are actually 8 gyms in Pokemon Silver, not 7. Here's the full list of gym locations:

Kanto:

* Viridian City: Grass-type (Brock)

* Pewter City: Rock-type (Brock)

* Cerulean City: Water-type (Misty)

* Vermilion City: Fire-type (Lt. Surge)

* Celadon City: Psychic-type (Sabrina)

* Fuchsia City: Poison-type (Koga)

* Cinnabar Island: Fire-type (Blaine)

* Viridan City: Grass-type (Giovanni) (This gym is only accessible after defeating the Elite Four)

Please let me know if you have any other questions about Pokemon Silver!