All the elements can be found with a quick google image search - just sort by size to find the images with the best resolution. The layout would need to be changed if you want it to conform to common bumper sticker dimensions.
Below are links I found for the best images I could locate. I don’t know if any of them are subject to copyright restrictions, poting restrictions, etc.
Large image of all 4 men killed:
http://www.bookwormroom.com/wp-content/uploads/2012/10/Desktop2.jpg
Sean Smith:
http://imageshack.us/a/img543/8209/1seansmith.jpg
Ambassador Stevens:
http://dailyrepublic.s3.amazonaws.com/wp-content/uploads/2012/09/13a1-stevens-mug-cl1-705x1024.jpg
Glen Doherty (2 - very similar):
Tyrone Woods:
http://media.10news.com/photo/2012/09/18/tyrone_woods_1348036286764_138599_ver1.0_640_480.jpg
Obama logo:
http://wttg.images.worldnow.com/images/18985708_BG1.jpg