Hi,
Thank you so much for your message! Yes, finding the right motors on the market is a bit of a nightmare. I completely understand your frustration.
First of all, please check the catalog; I already have mounts for several motors here.
Currently, there are mounting parts for NEMA 17 and NEMA 14. While I don't use Pololu motors yet, I'm planning to try them out, which means I can create a part similar to the one I added to the post (for N20 gear motors). I still need to officially release the new parts, though.
I've also been trying out various Lego-compatible motors. Some are honestly terrible, but others look more promising, though I haven't had a chance to test them yet: