You can get empty vallejo paint pots. I picked some up when I placed an order from here
and tend to use them for galleria product and water effects which come in massive bottles because the dropper means I can better control how much I use. GW also (used?) to sell empty pots but I heard they were being discontinued so whether or not there'll still be any lef is another matter. Worth looking into if your LGS is a GW or a stockiest.
As for how to make the mix, you can use a syringe (which can easily be bought in a hobbycraft or some sort of craft store) and will help measure accurately if you're very concerned about that. If you're using an empty GW pot or something else with a large top, stick something like a stainless steel ball bearing in to help mix when you shake. If you're using an empty vallejo pot or something else that tapers to a dispenser, just shake thoroughly and use something like a cocktail stick to stir. A ball bearing may get stuck at the end, like a hamster water container, meaning you have to open it up and fish it out to dispense paint.