They dont make a cover persay. About all you can do is go with a new hub and after market wheel or have some arts and crafts fun with alot of fiberglass gel epoxy and try your hand at making one.
My brother had a tuned out ford focus and found himself strapped for cash so he (like a fuckin moron) sold off his airbags. It took us a while but we made a cover for the passenger side using a card board template and alot of f/g epoxy and he got a new wheel for the drivers side.
Airbag slot covers are not a highly sellable item for companys because if you want an airbag for saftey and it blows you take it and and get the airbag replaced. If you dont want the airbag you get a new wheel. There isnt a whole lot of people that tell themselves..."hey, I want to keep my stock wheel but damn that airbag all to hell"