I have a few suggestions-
1-Ann Marie Corgill's book called Of Primary Importance
had some really GREAT ideas and could extend your unit.
2-Anything by Katie Wood Ray-she does a lot of immersion and inquiry.
3-Lucy just put out a small book (inexpensive too) with extensions and ideas for 2nd graders:
Spending 3 months in Non-fiction seems like a really LONG time. Maybe you could do different types of Non-Fiction like new paper articles, book reviews, etc...In addition to How-to's and All Abouts...