I'm looking for sonic games for master system and 99.9% all of them is in europe in ebay and none in amazon.
What is other website that I can get them from america?
According to Wikipedia, all Master System Cartridges differ in style in every Region, so they won't fit in another Region Console.
After looking up "buy retro games online usa" on Google, I've found quite a few sites:
http://www.tradengames.com/ProductCart/pc/viewCategories.asp?idCategory=100
http://www.collectorscardsandgames.com/new/SegaMasterSystem.html
http://www.estarland.com/index.asp?page=SegaMasterSystem&category=Games