I made one and it works fine.
I just adjusted it till it fit the bow I was making it for. I wanted a dedicated stringer for a short KMag I have, so I made this one, copying my store bought one.
For the pocket at one end I used a piece of nylon tow strap, doubled over and stitched diagonally to make a cone shaped pocket. I made a hole through the webbing ends with a red hot metal punch, and tied in the cord.
On the other end I drilled a hole edgewise through a 1" square piece of flat rubber and threaded it onto the cord and tied a loop about 8 inches diameter, with the rubber block captive in the loop.
I used 3mm braided line and tied it to the length that I needed to fit the bow and be about right to step on when I was using it, adjusting it at the end tied to the web pocket.
The things you do when you live where there are no local shops to buy from, and the shipping would cost more than the merchandise...