Blackstone's Criminal Practice is available via Lexis+.
You can access the resource directly by searching for Blackstones Criminal Practice on CityLibrarySearch and following the link at the top of the page with the green arrow.
Alternatively, you can log in to Lexis+ using your City email and password. You will find Blackstone's under "My Sources" - "View All Sources" underneath the search box. Scroll down the alphabetic list till you reach Blackstone's Criminal Practice.