Finnish stamp literature has quite a bit of these (as North Ingermanland, Aunus etc. are Finnish related territories). Likely the key source for the North Ingermanland stamps is "Pohjois- Inkeri Filateelinen tutkielma" (translates as North Ingermanland - a philatelic study) by Harry W. Walli. The booklet was published in 1943, and has about 30 pages.
Also the Finnish Philatelic Federation magazine "Filatelisti" has had several articles (based on Walli's work, as well as some new research) of North Ingermanland stamps and forgeries over the years.
Re, Serrane guide... The original French title is freely downloadable from French National Library
http://gallica.bnf.fr (just search for author Fernand Serrane, do notice the original title was in 2 volumes and hence there are two separate files to download). If you can read french (or spend time with Google Translate), then you're going to have a real ball with it ;)
Varro Tylers "Focus on forgeries" is a really nice resource for worldwide collector. My only grief about it is "one forgery per stamp/series" philosophy (as most stamps have more than just one forgery out there). LOL.
-k-