While yes I agree that between the 2 Black City should be added, but the ROM used for PokeMMO is Pokemon White, which includes White Forest, Zekrom and old Opelucid City. The 3 possible solutions to this issue is to add in White Forest, make people use a Pokemon Black rom for Black City, or use my suggestion and skip over the area entirely. Though I suppose the devs could make it into a completely new area.