That container is about perfect. About a month ago I was looking for something like that. Took me literally 3 weeks to find one in NYC flower district and then had it shipped across the USA.
I have a similar idea to yours: I wanted a central island with a 'mountain' with plants coming out if it in a circular fan shape. I built the island and the mountain out of small black lava rocks, surrounded by white sand (I believe you saw my 'creation').
The problem that I run into is that the lava rock is not heavy enough: it is a pain to keep the mountain shape, and an even bigger pain to have the submerged plants to stay put. Having that pile of rocks hold emmersed plants (especially vertically) proved to be above my pain tolerance.
The very initial idea was actually to place a ~3" diameter x ~10" high clear container in the center, fill it with lava rock and plant the emmersed plants inside, and then build the island / mountain around it. I could not find such a container and decided to give the current construction a try.
Part of the difficulty with the central planter is that it has to have (at least in my mind) holes / slits to allow for some water circulation between it and the water in the main tank. So, finding a glass one with holes proved to be fruitless.
Given my personal dissatisfaction with the current build, I am back to my original idea of the central planter, but now with less haste and with more planning.
My current plan is to either find clear PVC pipe, cut it to the desired height and then hand drill the holes (not looking forward to that process) or to have one custom made out of Acrylic or similar material (not looking forward to the cost).
So, that's where I am at with my 'tank' - please keep my ideas secret