Very nice Vita wallpapers. I came across this thread as I was searching for new wallpapers and these were a nice find!
As for .MK2 wallpapers, were you still looking for any? I don't know if you remember hearing about the NIS (Japan) contest they had to make processor parts, but they were giving away zip files with 4 of the characters from MK2. In this zip file are 4 jpeg files of the characters on white backgrounds, as well as 4 .PSD files. In the PSD files, although the characters aren't vectors, they are on their own layer which is nice if you wanted to make any transparent wallpapers or wanted to import the characters onto a different background.
I tried to find the direct link, but it is no longer working (probably since the contest is long over). If you're interested in these, send me a PM and we can figure out how I can send the file to you.