Todesstoß (with sharp S at the end)
In capitals: TODESSTOSS (with double S at the end)
Searching for "Todesstoß" in the web, it might be helpful to use both alternatives (Todesstoß/Todesstoss), especially in mailorders! Here the search results can be even different!
If you're interested in some further infos about the special German letter "ß", feel free to inform: