Not sure where to get one, but i use a food grade plastic 55 gallon drum. I got mine from a vet associate of my wife a few years ago. Was used for industrial bleach. Since it's food grade, it didn't retain any bleach, i washed the crap out of it just to be safe though.
I bought a hand pump made for drums, and have my ro/di line dump into the drum. Then when i need water, i pump it into my 5 gallon jugs.
Works for me since I'm renting. Once i get my house, I'll build a more permanent and automated setup.
Good luck!