He's on deceasedonline as being in one of the cemeteries managed by Lambeth Council. You have to pay to find out which and the plot number. Don't bother with a map, I doubt if the ones they sell have any more information than on the free signs on the gate!
The free information says he's buried with 5 others which may mean it's a "common" grave shared with unrelated people and less likely to be marked. If you post the plot details here, or send me a PM, I may be able to assess the situation.
