I sat down last night to try to solve that mystery. A little background: Two years ago, I received a web notification from the manga Spiral ~Suiri no Kizuna~ stating that, "I'm going to be published by Tokyopop. Please take care of my 4-koma." And with that, it disappeared without a trace. (For those who don't get it, go here and scroll down to the third paragraph after the title and author information section.)
No, seriously, in 2005, Tokyopop announced that they had licensed the manga of Spiral, and were planning to release it. Well, of course they were planning to release it... they're not like ADV, who just stop in the middle of things because they were bleeding money. But an interesting thing happened on the way to publication: Spiral vanished, and for a long time I had no idea where it went.
Having recently renewed my interest in the story, and since it's so incredibly text-driven that an English translation would be a wonderful aid, even though the Japanese volumes do have furigana, I set out looking for it. I suppose I could regale for a bit with stories of the death traps avoided (fan pages with less information than I already had), but the bottom of the mystery is this: Apparently, there exists some licensing issue between Tokyopop and Square/Enix, still unresolved to this day. The alternative is that Tokyopop has actually lost all hold on the rights to an English translation of the story, though they haven't admitted such.
The unfortunate truth is this: English-translated Spiral manga isn't coming our way any time soon. If you've watched the anime through to the end (the ending is around volume six of the manga, and follows a different path, since the manga storyline that it was loosely based on did not end until volume eight, if I'm recalling correctly), start brushing up on your Japanese and see if you can get hold of the tankouban, because that's the only available option.
Now, to end on a light note, I should mention that Spiral Alive has resurfaced in serialization (I forget which monthly it's running in at the moment), and there are a couple of vague hints at a Spiral movie in the future as well.