eBay be the best bet as you just need universal seat covers or if you looking something particular you can get them made. Over here there are few places who can custom made seat covers they way you like and can also choose the material.
I wouldn't bother. I personally think they do more harm than good. Just making sure ur not dirty whem you sit in the is a far more effective way of keeping them clean.
I kept my first ek9 seats covered. Never again