Since breaking blocks is disabled in the Wilderness, you can teleport to a special Mining world to mine for resources.
The command to do so is "/mine".
There is a World Border set at 500 blocks out from the spawn point on each side, making the Mining World 1,000 x 1,000 blocks.
The area around the spawn point is protected, so you'll have to move away from where you spawn in before you can start mining. This ensures players can't be trapped at the spawn point.
This world resets on the first of each month at 6:30 AM EST.
Each time it resets the world will be different, so there may be different materials available each month.