I believe radiator hose clamps would work.  I remember seeing some coated in a rubber or black plastic that would look very much like the ones used in the pic.    If not you could cover 90% of it with electrical tape to hide the standard metal finish.
edit to add:
I searched and found these. Look very interesting and I believe they would work for your application if big enough to go around the 2" bar. .
	
Also, I've seen heavy duty zip ties. Maybe double them up on each side.
				
			edit to add:
I searched and found these. Look very interesting and I believe they would work for your application if big enough to go around the 2" bar. .
Also, I've seen heavy duty zip ties. Maybe double them up on each side.
			
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