The map was apparently made by Hitachi GE Nuclear Energy. The map is in the report by the Working Council for "Mid-and-long-Term Roadmap towards the Decommissioning of Fukushima Daiichi Nuclear Power Units 1-4". The Council met for the 5th time on April 23, apparently. Hitachi is a member of the Council.
The report is available only in Japanese, and I don't think the detailed debris map (below) was disclosed in the regular press conference (there is no mention of it in the "Handout for the Press" section of their website, either in English or in Japanese.
From the Japanese report of the Working Council, 4/23/2012, page 98 (I inserted the English labels):
No such map exists in the report for the Reactor 3 SFP, as their survey of the pool the other day was only preliminary, they said.