I've seen various bombes and have even eaten from the same. Cristopher's Bombe refers to a desert bombe that was served to James Bond with a real bomb in it (in the move).
I looked in Google, and Yahoo, but with few results. Most posts refer to the film, or to another one about a code breaking machine. But this post - Elaine's recipes: Bombe Surprise
Will give you a light bombe.
I would make this recipe, and a shallow lemon cake, or shortbread to act as a base. Then, make the bombe from the recipe, and scoop out much of the center so as to make it hollow. Put the chocolate into the bowl you just carved, and place the cake or shortbread over the opening to create the final structure. Invert onto a serving plate and cover with a chocolate ganache.
That should get you close. For the cake, or shortbread, add lemon flavoring.
Seeeeeeya- Chief Longwind of the North