Those kits, esp for the Desert Wines, seem to be pretty rigid in their ingredients and process. I seem to recall the chocolate and raspberry comes together in a single packet called a Chaptalization pack. To attempt to alter the ingredients without having made one of the kits before hand would be inadvisable. Basically, the kit is a wine kit with the sweet flavorings added when nearly done fermenting. Without the Chaptalization pack, you would probably get a 12 to 14% wine. If I recall, the finished product is only 16%, but does cause some additional fermentation. It finishes sweet.
But, sorry to say, upon checking, this kit appears to have been a limited edition.
To me, however, it does suggest a possible approach... buy an inexpensive tawney port such as Benjamin, and trying small amounts of cocoa or chocolate syrup that you were entertaining. Plus, you would get a higher alcohol content.