What are you putting said 18650 in? Is it an unregulated 3.7v mod? Is it VV? Tube or box?
There are a lot of factors to consider when buying batteries. Do you need IMR or protected Li Ion? Button top or flat top?
Either way, my go-to supplier for batteries is typically Super T Manufacturing, good prices, good shipping, and they're quick to respond. Then again I'm an AW and Panasonic user, haven't stuck a Trustfire/Ultrafire in anything in nearly a year.http://www.supertmanufacturing.com/id75.html