Gray literature is increasingly considered to complement evidence and knowledge from peer-reviewed literature for science-policy processes and applied research. On the one hand, science-policy assessments need to consider a diversity of worldviews, knowledge types and values from a variety of sectors and actor groups, and synthesize policy-relevant findings that are salient, legitimate and credible. On the other hand, practitioners and scholars conducting applied research are affected by the time lag and biases of academic publication processes. Gray literature holds diverse perspectives informative for science-policy processes as well as practical evidence unfiltered by commercial publication processes. However, its heterogeneity has made it challenging to access through conventional means for a literature review. This paper details one endeavor within the Values Assessment of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) to review gray literature using Google's Programmable Search Engine. In the absence of a standardized approach, we build on the limited experiential knowledge base for reviewing gray literature and report on the potential applicability of our strategy for future reviews. Gray literature review results contrast findings of our parallel review of academic literature, underlining the importance of mobilizing different knowledge bases in science-policy assessments, evidence-based practices, and applied research.