Sulfuric? pretty easily available, ebay if you have standards, bog cleaner if you don't (in all chance, there probably isn't going to be much in the way of any hideously noxious organics in acid drain cleaner anyway, I only use it for generating or drying gases, or for keeping moisture out of things in a desiccator, but in the UK, concentrations I've seen have ranged from 96% at the low end up to 98% H2SO4, its dyed, but for concentrated sulfuric acid anything more than a visual warning is rather besides the point, it isn't as if anyone is going to get desperate and try drinking it, like a gutter bum might with denatured alcohol, it isn't what you'd call reinforcing, from an ingestion point of view, assuming one survived to try it more than once, that is. And organics have to be fairly tough to begin with to survive being pickled in concentrated H2SO4. I've often wondered what that dye IS, to avoid being charred to a crisp in-situ.
Another option might be binding the water as formed during the esterification, either using an anhydrous lewis acid salt, or molecular sieves. Sieves would have the advantage of being available in pelleted form that could be filtered out by more or less anything that the solvent won't melt.
