I have found my tubs at a local walmart. I would also try looking for tubs at Target, an office supply store (Office Max, Office Depot), or any type of bed and bath store (Bed Bath and Beyond). I am in VA so I listed names of stores that are local here, don't know what would be out your way but there should be similar stores there.

And honestly. I wouldn't trust just the latches that come on any of those tubs anyway. They are good at holding the ends secure, but the middle part of the lid will pop up. I use binder clips or bunjee cords to keep the lids on my tubs secure. I do have one latching type tub similar to what you posted a link to and the bunjee cords work much better with them (for mine anyway). The binder clips don't fit quite right over the edge of the lid and edge of the tub on my latching sterilite. I do have a basic lid sterilite that the clips fit very well over though.
I don't have any experience with housing milks in a tub, so I am not exactly sure what you would need to keep yours from escaping one, the bunjee cords and binder clips have worked for me keeping my bps in thier tubs though. Maybe someone with milk experience can help you out a little more with that.