Here are some of Dan Heisman's suggestions to get positions for Stokyo exercises.
"Go to most any Kasparov, Shirov, or Speelman Game"
How to Think in Chess by Jan Przewoznick and Marek Soszynski (at Amazon) -- I think this is the book (link on Dan's site didn't go to the book)
Genious in Chess by Jonathan Levitt (at Amazon)
Critical Moments in Chess by Paata Gaprindashvili (at Amazon)
Based on the reviews of the following book and the similar book by the same author, it looks like it may also be a good choice. Though it has a high price right now.
Imagination in Chess: How to Think Creatively and Avoid Foolish Mistakes by Paata Gaprindashvili (at Amazon)
Another book that I think might be a good one, based on previous things I have read about it.
GM-RAM: Essential Grandmaster Chess Knowledge by Rashid Ziyatdinov (at Amazon)
Any other suggestions or reviews of the above resources for this purpose?