Yeah, dunno about unbranded eBay stuff. Obviously, I am buy in Oz, but I would be quite happy to recommend a good US archery web site as a source. Victory comes to mind. Archery arrows do get hammered.
Caution: you can buy cheaper CF arrows from some USA companies, but they are pultruded. That stuff is utterly unreliable. Actually, that is not quite correct: its rapid failure under any bending load is quite reliable.
For a 2-man tunnel for extreme winter weather I have been using arrow-grade ‘2-D wrap’ shafts 7.5 mm outside diam. You can damage them (or anything) if you misuse them of course. Search on ‘storm guys’ here at BPL, probably under my name for more details.
I would have to say that 12.5 mm CF tubing strikes me as being suitable for centre poles on pyramids and not much else. It would FAR to stiff imho.
Cheers