Looking to buy a proper inrunner or outrunner motor, 3000 W minimum. A built-in ESC would be a nice bonus, but it’s not a dealbreaker. Prefer a seller located in the US or somewhere in North America.
As I know from trying to do the same myself… that’s pretty hard 
Your best bet is second-hand, ebay mostly, always keep half an eye on Mercari too. For an efoil what you want is a 140kv model Flipsky 63100. 190kv is far more common, but I’ve heard it’s much worse for efoil. After many months of keeping an eye out I finally did pick up a 140kv one at a bargain price from eBay, it was actually brand new in box. I might offer to sell it except that I know just how rare they are from trying to get one (without shipping from China) and I would have to have an extremely good offer to part with my only suitable motor for the efoil I will someday build when I have the budget 
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I still have not been able to find any US distributors for a <190kv 63100 outrunner (except ones at exorbitant prices from high end eskate stores). Hopefully someday someone will start a US retail business for DIY motors, maybe me… in 10 years XD.
P.S.-- on the off chance you wanted to be a beta tester for a 190kv one… those are readily available both from eBay used units and new directly on Amazon. From all I’ve heard though you would need quite a lot of current to use that if it would work at all.
You’re right, there are tons of 190kv motors on Amazon. But they don’t really work for me since I’m using a high-voltage battery. I’d prefer something closer to 100kv.
Curious on why going with the Flipsky 63100 vs a flipsky 65161 motor?