You can get any Avenger you want in Samsung's new Theme Engine, as long as that character is a dude.
Samsung's marketing deal with Disney/Marvel includes, among many other things, a special spot at the top of the Theme app for the Galaxy S6 and Galaxy S6 edge. These Avengers themes aren't wildly different from the other themes Samsung offers, save for the giant "only in theaters" branding for the upcoming Age of Ultron in at least one of the two wallpapers that come with each theme.
But if you're looking for the complete Avengers roster — as far as the Marvel Cinematic Universe at the end of the first Avengers film is concerned — you'll find one character missing.
The six Avengers themes in Samsung's app offer you one theme for each of the four big names currently on Team Avenger, as well as a theme for Age of Ultron and a theme for Hawkeye. While it'd be understandable if Black Widow and Hawkeye were both left out of these themes, it's a little silly for Black Widow to be the only Avenger not represented.
And don't even get me started on the lack of an Ultron theme. Villains need some love, too, Marvel and Samsung.