Who
The manga was written by Hiroyuki Takei and was published in Shueisha Jump (cant remember the date >-<). It went for a couple of years and ended in 2005... An interview can actually be found with Takei in two volumes of Jump. He was born May 15, 1972, and worked as an assistant to many famous mangaka, including Nubohiro Watsuki ( Rurouni Kenshin) and Tamakichi Sakura ( Shiawase no Katachi ). He won the Tezuka with his one shot, Itako No Anna (Anna is his main character as in signature wise). His other popular work was Butsu Zone. Shaman King was his most recent manga, until of course it ended :D. What do you have in store for us next Takei?
MANGA:
Shaman King has been translated into MANY different languages. In Spanish, French, Japanese *of course*, English, Chinese, and more. So far, all of the other languages EXCEPT English are very far if not done. English Manga is being published in SJ, and also in graphic novel format by VIZ. So far, it is on Volume 6 in Graphic Novels.
ANIME:
First! Know that the Shaman King anime is really old, and diverged from the manga at around volume 18. It has a totally different ending etc. Anyways, the anime can be found almost anywhere and has already aired in many different countries. In English, its airing on FoxBox as edited, but the DVD's can be bought from your local anime/manga store. Just check out Shonen Jump, since it's in charge of it with 4KIDS. So far, they are on the 2nd DVD.
UNLICENSED
Scanslations:
Since Shaman King is already licensed, it is incredibly hard to get hold of scanslations. HOWEVER, there are still some available. Several fan sites did the earlier manga, like Manga Screener, Aku Tenshi and many others. The known people still continuing it however, are Manga Rain who are currently around Volume 17 (Ch 150). ALSO, TAA (The Anime Archives) did the Osorezan Revoir (Volume 19-20 that deals with Anna and Yoh), so you can find that on IRC.
Translations:
There are summaries and translations available with limited amount of scans on various sites. The place I like to look is Shaman King House and MessWorld where Windera and Ruri translate.
Scans:
Basically scans are INCREDIBLY hard to find. Recently Greedland has taken down their scans, so you will have to hunt elsewhere, just look through forums and hunt around. One Place I might recommend for later chapter scans would be Great Spirit! its an awesome site with several different content! Also, the new manga section has scans of the chapters in Chinese for direct download, taken from Greedland.