If you Google “Peter Temin economics of antiquity,” the book seems to exist (Princeton University Press 2011?), but none of the clickthroughs seem to yield anything. I call them Google ghost books. If PUP clears this up, I am happy to pass along the answer. The mere fact that I would Google this at random suggests there is a strong demand for the book, from me at least.
In the meantime, here is Peter on financial intermediation in the early Roman empire (pdf).
Addendum: I am told that a real, non-ghost book will come out in the Fall of 2012, exciting news.