i must admit that chibokko might be right, however, i would check into the nuku nuku series, chobits, or hand maid may,
try doing a google image search for mecha and cat.
if you know where it's from, try contacting the author, they usually know where they've seen their
subjects.
looking through a list of anime ( directories, anipke, animenation, et cetera... ) for cat-girl, mecha, or other
related terms. i've found artists who have stopped drawing their old art, and recovered lost data ( via the way
back machine ) from just a watermark in an image i've downloaded from Kazaa.
it may take a while but don't give-up, it took me two weeks to get all of skribblekid's old h-poll art.