Yes there is mistertee2, to be specific - Toolbar Buttons can be created to do this...
You will need the Plus Pack to do what you want (as far as I'm aware that is - note: I have not done any of this myself - I'm merely providing the procedures that I can find that are applicable to your query regarding creating a new Toolbar Button.)
A little background (not necessarily directly specific to your question) before getting to the details of adding a "Deleted" (messages) Button to your Toolbar.
Among other things (i.e. advanced Voice Notifications, RSS protocols, Remote Folders, etc etc... the Plus Pack (linked above) provides the following "Sent Mail Viewer" (SMV) Interface (included in the Plus Pack):

- Provides access to various folders that can be added as desired (you can click on image to enlarge and return back to the forum topic by using the browser "go to previous page" button)
(note: As you can see in the screen-shot, I have added additional folders than just the "Sent" mail folder - i.e. a "
Deleted"
folder that you're interested in among others). I personally
use this (Sent Mail Viewer) Interface to access any one of the specific folders as opposed to adding individual (folder) Toolbar Buttons to do this (personal data has been redacted from screen-shot).
Now to your question about adding a specific (folder) button to your PP Toolbar - in this case a "Deleted" message button.
Here are links regarding creating Toolbar Buttons (among other things):
To start there is the
Custom Icons page. On this page you will see the link to "Toolbar buttons" at the top - clicking on this you will be directed down the page to the relevant topic. At that location you will see a "Custom toolbar ID reference" link. Clicking on this link you are provided with more details on the
Custom Toolbar page such as: you will see (by scrolling down) a reference to "33302 Open the Sent Mail Viewer and open the 'Deleted' messages for the selected account" which represents the "id/text" specific to a "Deleted" (messages) button (
that I would presume incorporates the data available in the SMV Interface (screen-shot above) that would in your case include the "Deleted" messages folder in the event you have added the (Deleted) folder to the Interface (as you notice I have).
As mentioned, a specific "Deleted" messages Toolbar Button is not something I've added personally (since in my case, the SMV Interface is sufficient for this) - so I hope this works in the way I'm assuming it does.
Let us know your results.