Could do with more info to help you.
Like, where do you sit on quality vs price? And do you really want to make a 100 x 18650 cell pack? If so, what's the series/parallel arrangement you're thinking?
Is there some other kind of fundamental battery size you could be considering? Maybe something out of an electric vehicle?
Do commercially available 18650s come with cell protection? The only ones I ever bought outside a pack were not protected. But yeah, like blueskull already said, you need to protect the pack abs of each cell has protection you probably need to remove it... So maybe worth dealing with someone who can build the whole thing for you.
Anyway... With no other info, I'd ring master batteries for a start.. though they will only talk to you if you have an ABN. And they won't be cheap, but they will have good stuff.
Battery world could also be good to ring?
Other than that, hobby shops and eBay and Alibaba (where I have surfed non protected 18650s before). It depends on how cheap and crappy you want your cylinders of volatile chemicals to be.
If you buy batteries online for air freight, you need to keep the total capacity of a shipment under 100Wh or you'll have all sorts of fun.