LEED requires specific SRI values based on product or material—no exceptions. Your first step is to try reaching out to your product manufacturers to obtain this information, or searching for any SRI values that might be applicable, if your material is generic. If this cannot be found, your next option is to send your material to a lab to be tested. Getting this data can be hard with existing materials other than concrete. Finding a similar product and comparing it to yours with images will not be accepted.