You can purchase Bakels 'Whip n Ice' it's is frozen and in a yellow carton that looks like a milk carton. The taste is nice and has a soft hint of marshmallow. If you Google Whip n Ice and click images you can see a photo of the carton and find a retailer close to you.
There is another brand, also frozen in a carton which is plan whit/off white colour and it tastes like ice cream but I am not sure what it is called.
I live in Sydney Australia and can purchase this from my local cake decorating supply shop.
Hope this helps