onemanga and mangafox.com both have the series :)
Manga2u.com works, too.
arisa
If you are talking about the shoujo ARISA then there is no anime coming out for it --- No one in the company has decided to start an Anime for Arisa.
You're looking for Arisa by Natsumi Ando, in which Tsubasa imitates her twin sister Arisa to find out why Arisa attempted suicide and eventually discovers the secret of the King.
List web that you can read manga
this manga can be read for free at either manga fox, one manga or zen manga :)
You can read all the chapters of the manga in manga animea or manga fox.
You can read it at mangafox.com (so far they only have vol 1)
you can read translated Earthian manga at http://mangafox.com/manga/earthian/
Arisa Mizuki's birth name is Mizuki, Arisa.
You can read it at mangafox.com .
You can read the manga at this website; mangahere.com
Try manga fox