Thanks Randen and Mike. I spoke with Kelly at Viessmann a few minutes ago and they are only selling the replacement tubes for existing systems and no longer sell the equipment. He said they are hooking me up with a dealer in my area.
Below is what the clamps look like. I made sure the copper receiver at the manifold for the evacuated tube collector was clean and smooth before I placed each tube in its spot and then used the clip to fasten them in.
If they are breaking when they expand, maybe I should work the rubber clamps closer together so that when they do expand, they are not under pressure in the wrong direction? Or would I put some kind of grease on the clamps to allow it to slide a bit? Something that would hold up in the weather and sun?
It is curious why they didn't break when they were originally installed and sitting stagnant in place for a year or more before they were relocated.