Fajita kit

Hello,

I am from the UK and absolutely love fajitas - old el paso style! I see i can buy fajita kits here but i cannot find the sauces to go with.
I can make guacamole and i'm sure i could make some kind of tomato salsa - but what is the Brussels equivalent to sour cream?!
Can anyone help - i sooo want a fajita!

Thanks.