Here are a few brands that are fat free. I get the one that is at the shop I'm in at the time!!! Good luck with finding them, you shouldn't have a problem, as almost everywhere does sell it, usually in pots of about 500g.
Aldi Be Light Natural Yogurt Virtually Fat Free
Asda Good For You Natural Yogurt
Morrisons Eat Smart Diet Natural Yogurt
Sainsburys Be Good To Yourself Natural Yogurt, Virtually Fat Free
Tesco Light Choices Natural Bio Yogurt
Total 0% Fat Free Greek Style Yogurt
Yeo Valley Organic Fat Free Natural Probiotic Yogurt
Hope that helps you find some!
Emma xXx