Many papers and posters presented at conferences are never published. However, they may be cited by people who attended the conference or got a copy of the paper from the author or discussant or someone else who was there.
Sometimes you may find that the author has published the substance of the paper in a later work, meaning that you no longer need the conference paper. However if this doesn't apply, you can:
Web of Science indexes the published literature of the most significant scholarly or scientific conferences around the world.
ProQuest databases also have some conference reports listed. Use "conference report" as a phrase search, preferably specifying a title search rather than just general keywords, and combine with the topic concerned. For instance: "Conference report" AND "genomic*".
In Medline and other Ovid databases, the Search Fields function can be used to choose Title (and Abstract) to then search for "conference report" in those specific fields.
Google Scholar can also be used to search for conference papers. Entering 'Conference report' as a phrase search in speech marks, alongside the topic or title concerned, also as a phrase search, should bring results. Alternatively, try the Advanced search feature, with conference report in the 'exact phrase' line and the required topic or header in speech marks in the 'all of the words' line.
ProQuest databases supplied under licence by Clarivate Analytics to University of Birmingham.
Google Scholar open search engine by Google.