Prusa support should be able to send you a spare pulley.
The closest replacement i've found - in fact the only one that i've found that will work - is the e3d hobbgoblin.
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I modified the power supply cover SCAD so that it can work with pretty much any power supply. Unfortunately it's a bit too complex to put in customizer on thingiverse, but, if you can use a text editor it's pretty straightforward to make your own with my scad file. PM me if you want the scad. My PSU...
I asked my seller on aliexpress to make a custom length leadscrew motor - 320mm instead of 300mm and they were happy to do that, and didnt charge me any more.