There's plenty of other concentrated flavor makers, but this was the only one I saw that offered online ordering. The rest want you to contact them first and get quotes, etc...which screams "MEGA EXPENSIVE" to me (or you must buy in bulk).
This place has very reasonable prices, and make sure you look thru all their flavors, there's some surprises in there too. There's stuff like Eggnog, Ginger, Horehound...some interesting stuff that might open up some new flavors.
Also, take note that none of this stuff is sweetened....which I would think is good because you can sweeten to your taste, but you do need to buy a sweetener as well.