this vendor makes tanks, I'm sure a dosing container would be easy: https://advancedacrylics.com/pages/get-a-quote . what are your "specific needs"? maybe we can help you find something already made for significant cost savings.
I just need a larger container and the available space to put it is quite tight. I only have about 7inch side to side clearance. I have a large ~4 gallon Tupperware container which works but I have to fill it up pretty frequently. It’s for dosing Kalkwasser