Digging tutorials are how you create secret foundations in Pokémon Brilliant Diamond and Brilliant Pearl. You'll need these if you want a place to place your statues to increase the chances of specific Pokémon appearing in the Grand Underground as you explore it. Diggers are consumables. You'll get more if you want to build additional bases during multiple explorations of the Great Dungeon. Here's where you need to go to get more diggers in Pokémon Brilliant Diamond and Brilliant Pearl.
You will need to find one of the hikers walking the Grand Underground. You can find them as you run between the various biomes that appear in this region. Talk to the hiker and ask him for the "Get goods" option.
You will pull up the hiker's available inventory. They should have digging drills for eight blue balls. You can get these blue orbs by digging at the fossil points in the Grand Underground, which are the orange icons on your map. Approach these locations to start the mining minigame and hopefully leave with some orbs. You can find several unique orbs, such as Red, Blue and Green.
Mining mini-games are tough, but the more you explore the Grand Underground, the more opportunities you'll have to get them to create secret bases.