It isn't as easy to find as you would think! I too thought Tractor Supply, nope, Lowes, nope, Ace, nope, ended uo using a more rounded "C", that is readily available.
It works fine. If you had to have one exactly that size you could go to any of the above, secure a piece of all-thread, bend to suit, or, a piece of roll stock, and a threading die, same process, and a little neater...I'll stick to the stock "C's" as long as they fit...
Back to a 5'er after 4 yrs fulltime.
Pulling with a '14 2500 ram, 6.4 Hemi.
Montana High Country 31RE