Did you not find enough good-quality sources? If not, go back one or more stages in your search process. Check, for example, whether:
you should make your question more specific or more broadly based
you have used every important search term
other suitable databases are available
you have combined your search terms in the right way
Tip: Not every sub-question can be answered by searching in literature. The reasons for this could be:
A subject is too new: there are simply no publications that deal with it yet. If there are, however, any ongoing research projects on the subject, you could try contacting the researchers.
The answer to your question is confidential - it may concern sensitive commercial information, for example. You could try approaching businesses, in this case.