AILA member Charles "Chuck" Miller (a former INS attorney) managed to obtain much of the current IFM through a FOIA (Freedom of Information Act) request. (Ongoing; he is still negotiating with CBP for further releases.) He has posted it to his website, linked here. Large PDF file: 354 pages, almost 2MB, so download may be slow depending on your connection. Fully searchable with Adobe Acrobat. Chuck says Ch. 15 is especially interesting. Kudos to Chuck for getting this info and posting it! Way to go, Chuck!
See http://www.millerlawoffices.com/publications and scroll down to CBP Inspector's Field Manual.