If FT says they are authentic, they probably are. I've never gotten batteries from them though. Hopefully, one of the vendors that @IMFire3605 listed will ship to you.
My battery says different. View attachment 485438
Just remember and be careful, that 35amp label is a Pulse Discharge Rating, not a Sustainable Continuous Discharge Rating, which the CDR on those are 20amp CDR.
There is no such thing as a 35a 18650 battery! But there are more than enough vendors/suppliers that would like you to believe that there are.
They could print their wrappers to say that they're 100 amp batteries, but the cell would still be whatever is under their wrapper.
Several people here and on other forums test, extensively claims of what a battery is capable of.
Examples of such testing from @Mooch 's blogs here ->
Mooch's blog | E-Cigarette Forum
At those power levels, and up to about 60W, you can use the 3000mAh LG HG2 battery. I don't know how long it will last you before needing charging but it's the highest capacity (mAh) battery you can get to use at 18W-35W.
Maybe try Illumination Supply or RTDVapor or even Orbtronics.
I use both and vtc4 and see no major difrenceSamsung 25r ( green wrap ) 2500mah
LG HG2 ( brown wrap ) 3000mah
Try these:Unfortunately not shipping to where I live.. Not even FT