pillsbury also has a version on their website these days, but i suspect the one linked above would be a good option. at least a few bloggers have substituted jiffy's fudge frosting mix instead. but, while i'm not against anything some might describe as "chemicals," i find those premade and boxed frostings just never taste as good as building one yourself. since the original ingredients are no longer made, anything you make will be a different version, so i'd go ahead and use the actual chocolate suggested. especially because, no disrespect intended, you're making quite an assumption about those four basic ingredients; i imagine that the mix was probably sugar, crisco, maltodextrin, and cocoa. maybe with some emulsifiers, salt, and flavour.