Do you have the hobby stores (i.e. Hobby Lobby or Michael's). If so, I found mine in the cake decorating section. It is made by Wilton. At first, I was completely over looking it because I was expecting, well I'm not sure. It is a small see-thru bottle, 2 fl oz., with a white cap. Now the label and color of the liquid will vary depending on the flavor (the butter is slightly yellow). Some have said that they found their's in the cake section of Walmart - I didn't look there as Michael's is closer to me and that's where I went first.
For dripping the liquid, I use a syringe that I got from the pharmacist when my kids were ill (a medicine dropper) If you don't have one, I know they are sold OTC in any Walgreens, Walmart, Target, Rite Aide, etc. It's really thick stuff so I just suck a little up into the dropper and gently squeeze until I get some out. BTW, I drip on an old cart, not directly on the atomizer. Don't know if that matters, but I'm just trying to tell you how I am doing it...
Oh, and they sell some dropper bottles at Michael's, although they seemed quite a bit bigger than the little bottle of glycerin...although it would probably still work just fine.