Don't know what city you're in, but ice cream cake blanks can be homemade by buying ice cream powder at a food additive store, beating it according to the directions using a fresh milk machine, and then freezing it in a mold.

Or you can buy it at a food additive store, usually they have it, or at least know where to sell it!

Or you can go to a specialty ice cream store and buy large tubs of ice cream and come back and mold and freeze it yourself!