You can't actually get an Awakening Stone in Pokemon Diamond. Awakening Stones are a new item introduced in Pokemon Legends: Arceus. They are used to evolve certain Pokemon from their Hisui forms to their normal forms.

However, Pokemon Diamond has its own unique evolution items that can be used for evolving certain Pokemon.

Here's how you can get some of the most common evolution items in Pokemon Diamond:

* Dawn Stone: You can obtain a Dawn Stone by trading a Snorunt to a certain NPC in the Veilstone Department Store.

* Dusk Stone: You can obtain a Dusk Stone by trading a Misdreavus to a certain NPC in the Veilstone Department Store.

* Shiny Stone: You can obtain a Shiny Stone by trading a Togepi to a certain NPC in the Veilstone Department Store.

* Ice Stone: You can obtain an Ice Stone from the Snowpoint Temple after defeating the Gym Leader.

* Leaf Stone: You can obtain a Leaf Stone from the Eterna Forest.

* Fire Stone: You can obtain a Fire Stone from the Fuego Ironworks after defeating the Gym Leader.

* Thunder Stone: You can obtain a Thunder Stone from the Valley Windworks after defeating the Gym Leader.

* Water Stone: You can obtain a Water Stone from the Lake Acuity after defeating the Gym Leader.

You can find other evolution items like the Everstone and the Metal Coat throughout the game, often found in hidden spots or as rewards for completing certain tasks.