Ghana Linguistic Diversity Resources
African Languages: An Introduction(a recent-ish reference book, with maps, to get you started - on the shelves in Canaday 1st Floor)
Ghanaian language listings with various additional info included:
CIA World FactBook - check out the Languages section on the Ghana country page... most interesting is to go to the Dynamic Statstics Tables (just click on the Languages link from the Ghana country page) and cross-compare Languages with other variables like Literacy, Ethnic Groups, Administrative Divisions, etc.
Ethnologue: Languages of Ghana - includes speaker population, region, alternate names, language family and dialects, plus link for more information
GhanaWeb: Ghanaian Languages - includes detailed info for government-sponsored and non-government-sponsored languages
Wikipedia: Languages of Ghana - a basic listing of government-sponsored languages, may help you make sense of the family relationships
For scholarly journal articles -- In addition to the general social science and Africa-specific databases linked from your course guide, check out Linguistics & Language Behavior Abstracts (LLBA), a linguistics/language specific journal database.
Some potential search terms (play with them to modify the number of search results you get - add terms with AND to get less results, add terms with OR to get more results):
ghan* AND (language* OR linguistic*)
ghan* AND (language* OR linguistic*) AND divers*
"northern ghana" AND (language* OR linguistic*)
Don't forget the Dagbani-specific resources I suggested in a blog post last week.