State Constitutions Illustrated is a collection of the constitutions of the 50 states of the United States, together with related documents and resources. Containing the text of every constitution that has been in force for every state with the original, consolidated and current texts and an extensive collection of documents from before statehood. (Hein)
You can also find state constitutions in one or more of the following places:
Links from the state legislative body’s website (FREE)
In the state resources collections of commercial legal services like Westlaw, Lexis, Bloomberg & Fastcase.
Print copies of state statutory codes often include that state's Constitution. If annotated, that may be an inroads to finding caselaw based on its provisions.
State Constitutional Law in a Nutshell by 