Join the club. I put in 600 sq ft years ago and need to replace some tiles. might get lucky and find something close since most of it is under the frig with only partial tiles showing. let me know if you have any luck!

I found some on Craigslist, it was accross the country in FL. I kept googling trying different combinations of Ceramiche d'italia in quotes, adding med slate grey in quotes until I found some. She had 4 full boxes and a couple partials. I bought the partials and it cost me more to ship them than the tile cost. Note that it is also called gregio which is grey in italian.
I also missed out on a couple others that were listed on craigslist.
you also might try creating a google alert that will search for you and email you results everyday.

good luck.