There are a ton of jockey pulleys here on Thingiverse, but most of them are the older 11t design. I recently managed to smash up two SRAM jockey pulleys (no idea how, the derailleur was fine) and I found out that replacement pulleys were $30 - I decided it was time for me to add to the growing collecting of Thingiverse jockey pulleys.
For some reason, SRAM thinks that jockey pulleys need the narrow/wide design that is so wonderful for chain retention on chainrings. Don't know as it really helps anything all that much, but hey, whatever, I matched up what they had and duplicated it as best as I could.
I have the raw model included, as well as a split model which can be printed in halves and then superglued together. I've found supports on the whole model to be annoying to clean up, so the split halves and superglue winds up being easier.
This version is designed around the 626 bearing that SRAM uses in the X-Sync pulleys, and includes two press pieces so you can press out the old ones and press them into the printed replacement. (Reuse the SRAM end caps) However, it seems that the 626 bearing is less common, so I'm going to try creating a version using the more common 688 bearing. That won't work natively with the SRAM hardware, though, so this version should still be useful.
Update 8/21/18: After over 8 months and 1750km (1100 mi) on the MTB through winter, spring, and summer, I pulled off the lower pulley which I printed in PLA (the one in the original photo) and cleaned it up and was pleased to see it was in excellent condition. See the photos that show some wear but not too much. Only real issue was the bearing bore had opened up a bit which allowed the pulley to move side to side, thus the wear on the face. I'm planning on recreating the pulley in Fusion 360 and will address the bearing fitment issues in that redesign.