I bought about 1/3 of a ton of mixed sizes and profiles from Skagit River Steel in Burlington , Wa. [1 800 869 7097]my nearest steel supplier. They got it from Ryerson Tull. It was a bit spendy but nice stuff, particularly in 20' stock
It's an easy profile to make, particularly in shorter pieces;grind ,forge,or machine the desired profile in a block of steel, ease all edges , mount on a 50- 100# plus hammer , heat appropriate size stock to fill the void and hit with flat top die or tool, repeat .... keep scale out of the die cavity for a clean finish, straighten stock and trim flash ,reject mistakes and make extra while you are at it.