Does any one know where i can but the manga Mirai Nikki Mosaic?

Sorry but i don't think it has been translated into English, not yet anyway. I have checked some well known manga distributors, anime/manga merchandizers...nothing :( I'm not all knowing so toi never know...

If download ok why don't toi try mangatraders? they have large collection so may be toi will find it there. best of luck

Sorry to say it hasn't been released in English, and is unlikely to be released any time soon, possibly never.
The company that was releasing Mirai Nikki/Future Diary was Tokyopop, who closed their North American publishing operations last year. So they are no longer releasing manga in English (still releasing manga in German though).
Although I am not sure if Tokyopop even had the license for Mosaic, even so all rights went back to the original owners. So if there is any hope, toi will have to wait for another company to buy the license, ou read it online.

R.I.P Tokyopop