I can help you with this as I made my own pulley based on a design on Thingiverse. I “motorised” some vertical blinds years ago, using an Arduino and steppers and which uses a chain to rotate the slats and a cord to open and close them. I used three LDRS set in tubes at different angles to detect the direction of the sun and rotate the slats accordingly but I digress…
The search term you need on Thingiverse is “Parametric ball pulley”. That should bring up a few designs. If you don’t have any joy with that, I can supply you with an Open scad file that you can use to generate an STL for whatever dimensions you want. If you don’t have OpenScad, I can let you have an STL for the one that I made. If you don’t have a 3D printer, I can make you a pulley for nothing but you’d need to pay the postage (I’m based in the UK). Let me know.