If you are unable to locate an SDS in the substance database when creating an assessment, you can raise a request for Sevron to source it for you.
Simply follow the steps in this video:
How do I Request an SDS from within an existing document?
http://helpcentre.sevron.co.uk/en/articles/1537589-how-do-i-request-an-sds-from-within-an-existing-assessment