Through the support of the Wellcome Collection, images of the Bills of Mortality from their library are available here to browse.
Rights to the images located here are Wellcome Collection Attribution4.0 International (CC BY 4.0)
Volumes of the Bills of Mortality from other libraries can also be viewed at Early English Books Online (EEBO). EEBO is a collection of books on microfilm and digitized, available through subscription services at many libraries or at the Internet Archive:
Early English Books, 1475-1640
Early English Books, 1641-1700
To better understand the numbering and dates of the Bills of Mortality, review this overview of calendars: