Where do you get the Turtwig Mask in Pokemon Pearl for your accessories?

You can't get a Turtwig Mask in Pokemon Pearl for your accessories. There are no masks in Pokemon Pearl. There are only hats, and you get them by:

* Getting the hats from the Poketch App: This is the primary way to get hats in Pokemon Pearl. You can get them as rewards for completing different tasks in the game, like catching a certain number of Pokemon.

* Buying the hats from shops: You can purchase some hats from shops in the game, but not all hats are available for purchase.

* Getting the hats from events: Some hats are only available during special events, such as the anniversary events.

Keep in mind that there is no Turtwig mask specifically, but there are plenty of hats available in Pokemon Pearl.