There is this guy selling a decent JzP helmet, the liner looks complete and with some TLC, this could be turn into a nice M15 JzP, well, an addition of original M15 Chinstrap, proper EM kokaden will be nice.
It does looks like it has a M15 Kurassier spike top instead of a JzP spike top tho.
Some says its common during wartime years.
http://cgi.ebay.com/WWI-German-Helmet_W0QQ...1QQcmdZViewItem
Hope this helps,
Mush