I found this on the Sabong forum, a guy makes these I think:
They also sell them at Randall Burkey, at around $45 for 12
If you know someone who can use a sewing machine, they shouldn't be too hard to make.
I tried my hand at slapping one together using some materials that were at hand. I used an old nylon strap for the leg holder. I put grommits in the appropriate places (at each end). I used trimmer line for the cord with large trimmer line making up the stake loop. I saw after making this first one that the trimmer line might present dangers to the fowl if he gets tangled. Rubber cord seems to be superior.
This Rooster tie cord looks toyish due to the colors, but it's really strong. You can actually hang from it.
Shot a Rooster
Killed a Hen
The Hen Died
The Rooster Cried
And the Pullet Committed Suicide
struggle, suffer, endure, learn