It's sold in a half-liter tin bottle (like a PET-bottle, only from tin) -- see a big version of the bottle here.
We wouldn't mind drinking Aka Oolong at home either, so we went to the Simon Levelt and asked for it. Of course, they didn't have it -- they only have Oolong from Taiwan ('Formosa'). We got a little bag of all four Oolongs they had, brewed tea of them, chilled the tea, and tested.
Our methodological classes in Psychology have scarred us for life: we set up a double-blind procedure for the tasting. Only when the results were in, we looked at which teas were which. It turns out that we liked the cheapest one (the Formosa Finest Oolong, EUR 29.50 per kilo) best when it is chilled! The most expensive one (Grand Pouchon, EUR 89.50 per kilo) came in as a close second.
However, these are not the Aka Oolong we drank in Japan. JTI writes in their 2003 Annual Financial Results and Forecast (PDF):
Specifically, we started selling [...] and "Aka Oolong," which uses only highly fermented oolong tea leaves.
If this rings a bell with anyone, please let us know what tea it is, and where we can get some!