MrMatt, hold your horses! I recognise the reservoir that you refer to, and show in the picture. It is sold by
Cooling Solutions, a company in Germany. In case you don't speak German, on the site, select "Wasserkuhlung" on the left, and under that "Ausgleichbehalter".
It comes in various sizes, with or without plexi mounts, and accomodates LED lighting.
I'm sure they will accomodate you in sending an order to the USA.