Here in Australia, we have a fairly comprehensive array of flavours to choose from, and many are considered industry standards. However, there are a few flavouring companies that are only available if importing, generally form the US or EU.
Listed below are all the available concentrate companies and the vendors who distribute them.
Custom Australian Concentrates
I use a lot of their flavours and find them to be excellent.
Juice Whore Signature
They produce superb tobacco concentrates and more.
Their reputation is very good, but I have not tried them yet.