Hi,
I recently took MD MPJE in August 2019. I passed on my first attempt but walked out of the testing center thinking I failed for sure.
Being an out-of-state test taker, I found a limited amount of study material. I have purchased the University of Maryland law review/practice questions and Rxexam questions. I want to say neither of the material will fully prepare you for MPJE, but they were good material to start. I frequently went back to the law book provided by MD BOP to clarify things and I found this very helpful.
I studied for 2 weeks, but please keep in mind that I have taken MPJE for other states few years ago.
Best of lucks to you and hope this was helpful!