According to the game's official mailing list, Looney Labs is letting Aquarius drift out of print for the time being, so that they can concentrate more on their core products, like Fluxx and
This is kind of a bummer; when I first became a Looney fan around 1999, the game was their most recent release, and so it's always been closely tied to the company itself in my mind. It's the single game that best visually personifies the Looneys' "Hippie Game Company" self-image, with its colorful, Peter Max-esque artwork. And, while a lot of hobbyist-gamers I know roll their eyes at its many random factors, it's definintely the only Looney game that I can consistently get anyone in my family to play!
But, business is business, and I totally understand their decision. In the meantime, you can take Aquarius for a spin online at Volity.net, or via Kory Heath's Javaquarius. If you dig it enough to want your own real-life deck, your best bet is to grab one from the Labs' online store, since they've stopped distributing it to retailers.