Nothing to do with TFS, really. You just have to check in your dependencies to source control.
In your solution, add a folder called "Dependencies". Add a matching folder on disk in the same location in your solution hierarchy (annoying, I know). Add your dependent external DLLs to that directory.
![enter image description here](https://i.stack.imgur.com/3HxCU.png)
As these are now part of the solution, they will travel with the solution into source control.
Reference these in your projects. It will look like this
![enter image description here](https://i.stack.imgur.com/Gv0a7.png)
but it should be recorded in your solution file as a relative path.
<Reference Include="Example">
<HintPath>......DependenciesExample.DLL</HintPath>
</Reference>
If you're having problems with this not being the case, you can simply edit your project file and change the hint path.
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