Unfortunately, Google closed down Poly which was the database which CoSpaces was using for 3rd party 3D models.
To try and overcome this, before I send an assignment or CoSpaces task out to my students I try to add as many relevant 3D models as I can. This does take a bit of time; however, assists students in visually demonstrating what they are trying to communicate. I have had the most success with SketchFab Creative Commons: https://sketchfab.com/ I do not suggest sending this website to students as it is not filtered. Instead, upload the models into CoSpaces ready for students to use before sending them the task.
I hope this helps you out.