Take note here...
https://www.horizonhobby.com/prop-adapters:-power-110-160-eflm41103
If this is in fact the motor and adapter you now have, it's already drilled/tapped to 10/32 threads(internally) specifically for spinners with center-bolts.
After I thought about this thread for a minute, I started thinking about 12mm is big.. and I also didn't find anything in a spinner-nut that big either.. so I investigated further... and now it makes sense.. that 12mm shaft is large enough to easily be drilled/threaded for a spinner screw.
So now that leaves you to choose a spinner, and make sure it's drilled/reamed straight/center for that 12mm shaft. So a spinner with a center bolt will just bolt up... then you have the clearance to hone the prop notches if you need too.
I can see where a 4-bolt-hole mount spinner wouldn't work, as by the time you get your clearance, there probably isn't anything left to actually secure the cone. Does that make sense..? I think I'm getting it.. anyway.. check the above out and check the prop-adapter you have and see if you've got threads in there. If you do, they'll be 10/32.. from there just fabricate/cut a screw(preferably a hardened allen-head machine screw) to the correct length and go fly.