"Cigarette/Vape stores" tend to carry lots of 18650s and might stock 14500s as well. If you live near one you could stop by and see. Flashlight enthusiasts tend to be very knowledgeable about batteries as well and it's possible they use 14500 form factor. RC/drone/hobby type shops might have some as well, but I think they usually mostly stock 2-4s pouch batteries.
To concur with Qinti, too high of a capacity rating can be a big warning sign. It's usually better to buy Panasonic cells that are of smaller capacity, as they're more likely to be genuine.
If you're handy with a soldering iron, you can buy any pouch cell you feel like and solder it straight to the terminals. Not good if you were planning on carrying spares with you, but you could maybe rig something up with inline JST connectors.