Hi mate, welcome back.
I'm fair green with sabers compared to most, but my first came from battery world at $30. But after that I had a seller in eBay selling genuine Panasonic 18650 for $11 delivered. Other sellers sell clones that look similar.
But the 18650 can be bought at jaycar and other stores locally as well. Just always get the protected cells.
As for the 10 and 15 another batteries for neopixel blades, I'm still test batteries that I like.
When I get a chance later, I will put some links up.