There have been quite long threads on the 'film photography podcast' and 'I shoot film' forums on Flickr about kodak hawkeye surveillance film. From the photos I've seen it doesn't look much like portra. Higher grain and much higher saturation. People have described it as Ektar 400. Someone has been selling bulk rolls of it on ebay at silly low prices but shipping from the US wasn't economical for me.
All of Kodak's surveillance films have been discontinued but whilst poking around I also noticed that the B&W hawkeye 400 film looks to be Tmax 400 on an estar base. It has the exact same spectral response and development times. If you could find this cheap you might be on to a winner.