One helpful resource for your research is the Oxford Global Music Series, which has books devoted to specific music cultures. You can browse the list of titles in this series via the library catalog. Here's an example of one volume:
You can use the USU library catalog to find more books and ebooks on your topic by selecting the appropriate Material Type (in Advanced Search) for the resource you are looking for:
When searching RILM, you can use Major Topics to search for articles in broad areas of music research. If just keyword searching lets you down, combining a Major Topic with a keyword helps you refine your results more efficiently. Examples of Major Topics related to world musics include:
Look up the Major Topics associated with your research question on RILM's Classification System website.
Articles in RILM are also tagged with Subjects, which tell you more specifically what an article is about. You can also search by Subject to find more articles on that narrower topic. The following example shows how detailed subjects can be: