CANADA
Oh boy. Let’s start with this.
Due to very tight air shipping regulations regarding lithium-ion 18650s, most Chinese sellers will not take the risk to ship via airmail, or take the time via boat. Some will however.
In Canada:
Durenergy on eBay: https://www.ebay.ca/usr/durnergy01?\_trksid=p2047675.l2559
This is the only seller which will not gouge you with huge prices on 18650s and pay you for shipping. They only carry low drain 2200mAh-2600mAh 18650s, but will be suitable for most lights. They also carry 3000mAh 18650s, along with 2000mAh 20A 18650s, and 2200mAh 10A 18650s, which would be suitable for lights like the BLF Q8.
Outside of Canada:
Here we get in the real of what I like to call, vacation shipping. The only way to get cheap, high capacity high drain cells in Canada will be via boat shipping, which usually takes 1 month, up to 3 months. I’ve bought 18650s that way before, took “only” one month, but can take up to 3 as specified before.
Sunway Store on Aliexpress: https://sunway.aliexpress.com/store/group/Battery/3173029_512165822.html?spm=2114.12010608.nav-list.3.5d7d69d44E3rEx
I’ve bought cells from them, 6x Samsung 30Qs to be precise, and they test right on target at about 3000mAh down to 2.5V, have good low internal resistance, and still have great capacity at a 5A and 10A drain down to 2,8V(2810mAh and 2760mAh respectively). They also don’t stick out to other legit 30Qs that I bought elsewhere, with 3 poles on the negative terminals, and a non auspicious looking marking. They also make my BLF Q8 very hot 
Others have bought cells from them, and have confirmed them to be legitimate. Be aware though. They ship very slowly to respect shipping laws.
I’ve also ordered 2x 21700s 4000mAh from them recently to see if they ship out the same way, and if the cells are still legit 
Aliya store: https://www.aliexpress.com/store/1382210?spm=2114.12010612.0.0.7a5b23dbkNLBYu
Same thing. Other people have confirmed the cells to be coming from this store to be legit, with non suspicious terminals, not too low small unit pricing, and shipping fee.
I have tested both the NCR18650GA and Samsung 30Q, and can confirm that they sell completely legitimate cells for Canadians!
There’s also a new player on the bloc. He’s a member on BLF, and has his own store, 18650 Canada
https://18650canada.com/
Rejoice!
2021 update: Looks like the Sunway store doesn’t sell individual cells anymore. Sad.
Same for the Aliya store and even Lucky 