Where and how to get the brick to improve ratushi to 7 ur. (Kingdom Two Crowns)

To improve you must go into the iron age.
Spoilergate mine object entered in the Kingdom: Two Crowns. Appears on the 4th island. The construction of the iron mines is required for the transition in the iron age" with access to new buildings and units. Visually, the mine resembles a mine with veins of iron. Paying 20 coins will start the automatic construction of the mine without the participation of the builders.

The construction of an iron mine allows you to:
-Upgrade the walls up to the 5th level.
-To improve the tower to the 5th level.
-Improve the town hall to the 7th level.
-Build lighthouse 3 level.
-To build the forge.
The upgrade cost 20 coins. After you purchase an upgrade - will automatically run the process of construction of wall 5th level near the town hall.
Source: http://ru.kingdomgame.wikia.com/wiki/Kingdom_Вики

you need an iron mine, which is only on 4 islands