These are really easy to make, especially if you have a welder, but the welder isn't mandatory by any means... You just need a screen door roller set from Home Depot, a few nuts and bolts, and a small piece of angle iron.
I'm not sure if anyone's making them to sell but I can show you how I made mine or build you one if you want.
The difference is night and day with a roller in place and it makes the clutch a lot smoother and easier to pull.
I know Arrow Racing uses a different method that eliminates the roller but re routes the cable so it's at a better angle to the clutch arm so the end result is the same... a really smooth and controlable clutch.
Here's a few close ups of mine so you can see how it's built, mine is welded together but they can also be bolted together or you can braze it using a mapp torch...
Hope this helps, and hopefully somebody with the Arrow setup shows pics, theirs is easier to make and works just as good.