This is my favorite site for cooking emergencies http://www.thatsmyhome.com/recipes/food-substitutions.htm
This has subs for cream used for cooking as well as a couple ideas to make whipped cream. I've never tried any of them in frostings and it might take a bit of expermentation. My favorite frosting is boiled icing (7 minute frosting, rocky mountain frosting, etc)the ingredients are basic but it won't work to decorate.
The cocoa powder is most likely some funky form of "natural" (aka nasty in my opinion). The website above has conversions for substituting cocoa powder and fat for melted chocolate, the reverse also works. In some recipes it will straight sub in others you have to remove some fat and sugar and use a small amount more melted chocolate than you would need powder.
Depending on where you are things might just be called something different and it takes a bit to figure it out. The quickest route to getting it down is probably to find someone local or a less recent transplant to help you. Otherwise, experment until you get it right. Danish pastry was most likely made when some poor soul left the butter out of brioche and was trying to cover his tracks before his boss found out; Proof that not all "accidents" have bad endings.
