Nope you cant buy fabric from them they will sell you the complete seat for an insane amount of dollars... either look for another CE that has the seats already in the colour that you want or put the money towards getting yours retrimmed
I know Holden sells the covers, foams and frames seperately to renew seats. Give your Mitsi spare parts dealer a call and find out what they have but sit down when you get a price. It may be cheaper to get someone to re cover them for you
It will probably be cheaper to get all your seats front and rear re trimmed so they still match, but then it wont be a stock fabric pattern but it'll still look good. And you can just do the door cards yourself.
Jazza that was the other thing I was thinking even though I don't want to spend that kind of money, plus I want the car to have an OEM theme, so nothing looks modified