Looking for main scripture for shulini durga practice. Seems this is a rare form. Please guide
Indeed the ShUlinI durga and vana durga are not very common known worships. The upasana is considered an advanced stage hence the upasaka is generally asked to complete preliminary anushthanas before this one.
The details can be found in durga section of shArada tilaka. Also it may be available in mantra mahodadhi.
However, i got a book on this subject but it is in telugu language. Nevertheless if you can find someone who knows the language may be of good help. This is the online ShUlinI durga book