Can you find something similar?

If not, I would find a tile that picks up one of the colors in the existing tile.

I was going to suggest the same as Acrhitectural Novice. You may be able to find something special (that looks like a piece of art) that fits with the current back splash.

Agree it is an opportunity for a special "feature" and that is limitless in possibilities. If you have any good tile showrooms in your area take a sample of current tile with you and a photo. Get one of their designers to help you. Of course there is always something like tin tiles: http://www.decorativeceilingtiles.net/tin-backsplash-tiles/

IMO a tile feature behind a stove is avery dated look and can really only be done successfully in a huge mediterranean style kitchen

the splash is your opportunity to make this kitchen sparkle! and to bring it up-to-date at the same time...bite the bullet and replace it. you spend far too much time in this space [and in front of the stove particularly!] to stare at "make-do"...which is exactly what it will look like.

if not, pop off random tiles [AND the partial border!] and insert a complementary tile, using the 'pop-offs' and complementary tiles to finish the hole.

you will still wish you had replaced the whole thing :)