Did you delete them? They are no longer on the 3D Warehouse?
You cannot import through the Trimble Connect that is in the middle on the left when you open the hamburger menu.
You can only open a model from TC, it replaces the current model.
In Shop, you have access to two libraries or collections of components, one is the ‘in model’ collection (Little house icon), the other would be the 3D warehouse (with the search option)
In the PC version (Pro), you have a third option to look for collection of components, besides the ‘in model’ and the 3D Warehouse. These collections can be on your local hard drive, a google drive or netwerk server. You have to add them in the components panel in the tray through the little blue ‘details’ icon (open or create a collection)
You cannot access models directly in Trimble connect, thoug, the way you can with services as dropbox or google drive.
It is actually a good thing though, many problems arise and corrupted models this way, it is better to download first and work on the downloaded file (autosave) and upload when done.
Since components and materials are just downloaded once (and hen reside in the in model collections) problematic syncing with these files will not occur that much.
Trimble Connect is not just another cloud storage service, it is a project manager, where it is important to have the latest versions available for everyone in the project, in the (design office and out in the field. If the field team get’s a notification that the design team has published an updated version, they need to download it first.
The extension in SketchUp works similar, if you open a model, it would download the latest version, when done editing, you publish it back in the project.
That said, you can use Trimble connect as a plain storage for your components, but you would need to download the files in a folder on your PC and then add that folder as explained (little blue dteails icon in the component panel.
Note: if you download a folder, it is zipped, you need to unpack, first.
Alternatively, if your components still reside on the 3D Warehouse, you would have access to that collection through the icon in the large toolbar, or [menu]Window->3D Warehouse l