This channel is very easy to make if you have access to a sheet metal brake and if not take an undamaged piece to a sheet metal shop and they can make you one. We have our own brake and we have to make the bottom section on most of these in the AD truck. The brake will only bend it to 135 degrees (45 degrees past 90) so you have to tap the lip around with a flatface sheetmetal hammer until it is a tight fit for the windlace. Do a couple short pieces first because you will mess them up but with practice you'll get the hang of it. If you can't find a break that will make the second groove since the strip is so narrow, make two strips and stack them together. This gives the advantage of being adjustable since you can slide them together or apart to gain the correct width and then trim off the excess. We spotweld them but a countersunk screw or thin head pop rivet would work. Good luck

Evan