Is this manga popular enough during their prime? Cuz unfortunately it didn't adapted an anime... THIS is my favorite yuri series and it's quite frustrating :(
Other people around here are a lot more expert than I am on this topic, but my impression is that there's no incentive to do anime of an already completed manga series, and yuri just wasn't much on the anime radar at the time that such a series would have been possible.
I believe the Marimite and Strawberry Panic franchises benefited from starting as light novels and proving they had legs by branching into manga and other media before getting an anime.
That's my sketchy, half-informed take, anyway.