These days there are a number of good providers of electric skateboards parts the following are my thoughts and experiences.
https://diyelectricskateboard.com/
Been in the game of selling DIY electronic skateboard parts for the longest. Sell all parts. Nice motor mount at an okay price. They have single motor kits starting at $729 (less batteries)
I’ve personally purchase a VESC from them. Frankly I’ve has trouble with it but I don’t know if that was a motor issue of a quality issue which I’m still testing so not comment on their refund policy/quality at this stage.
https://flipsky.net/
Chinese based company more recently selling. Focused mainly on selling VESC both version 4.12 and 6 Vat a good price and motors. Their others components are a bit lack lustre.
Purchase from them previously they charge me $70 for shipping to “remote” part of the world (a large city in Australia)
http://www.diyeboard.com/
Chinese store selling kits and full boards. Awful website but they have a huge range of kits and parts. Selling more on the budget end. Don’t seem to sell VESC style speed controllers but other types. Single motor kits from $329.
https://www.mboards.co/
Relatively newer selling with a US base. Focused mainly on creating and selling battery packs but have most of the other parts you will need.
https://street-wing.com/
UK based they sell the full range on parts needed for your e-board build. Their own motor mounts, Torque board ESC and standard motors. No motor style parts sold. .
https://eskating.eu/
Selling out of Europe. Have kit, part, and motor mount designs. They have kits starting at $820USD
https://www.unikboards.com/en/
Focus is mainly on mountain boards. They sell complete boards, kits and parts. Higher end products selling out of Europe.
Maytech – selling through Aliexpress
https://maytech.aliexpress.com/store/1630416?spm=2114.search0104.3.12.d72b6e17V6mzFV
Pretty standard fare selling VESC and other components through Aliexpress. The mounts don’t look fantastic and you would think that the pricing would be a touch cheaper on Aliexpress. Kits from $602USD
Hobbyking
https://hobbyking.com/en_us/turnigy-sk8-esc-for-electric-skateboard-conversion.html
No. Just no.
Ebay & BangGood
https://www.banggood.com/buy/electric-skateboard-kit.html
You can also buy parts off ebay (surprisingly found good pulleys) and BangGood